As you read this article, nestled snugly in your sofa with a nice cup of tea or lying on your lawn with a Pimm's and a croissant, I'll be hard at work, striving to maintain what is arguably the most ambitious world record attempt in history.

I've always wanted to get into the Guinness Book of World Records. As a boy, I dreamt of becoming the World's Tallest Man, inspired by the gangly 8ft 11in frame of Robert Wadlow peering out at me from my favourite book. But by the time I reached 30 years of age, my own body had ground to a halt at the measly height of 6ft 2in. I was forced to move on to the next major title. I knew I couldn't be the World's Fastest Man, and I didn't want to be the Man With The Most Bees On His Face. So I went for the big one. I resolved to become the Oldest Man In The World.

So far it's all going smoothly. I've been steadily climbing the world rankings for the past 31 years, 10 months and two days. When I was born I was last. I was literally the worst person in the world at being the Oldest Man In The World. But after three and a bit decades of staying alive I have managed to move up 3bn places. I may still have some way to go, but these are impressive statistics, especially considering I only decided to really go for it a couple of years ago.

Until then I was living a happy-go-lucky lifestyle, taking each day as it comes. Not any more. Now I look after my body and plan for the future. This is no time for fun. Fun is risky. I even have a sponsor in Innocent, the folk who make the healthy smoothies and who are providing me with vitamins and £1,000,000 when I reach 150 years old. I'm an athlete, like Roger Federer or Tiger Woods, but with far loftier ambitions.

It all started as a bit of a joke. Having watched David Blaine audaciously sit in a box for a month, I thought it would be funny to announce that I, Alex Horne, was attempting to live longer than anybody else in the entire world. Take that, Blaine, I thought.

But the more I talked about my simple plan, first on stage and later via a dedicated website (longlivealex.com), the more complicated it became. Advice appeared on the site. People began to follow my progress and offer me support. My attempt had become official. People wanted me to succeed, and I owed it to them to take my prospective longevity more seriously.

I should state for the record that when I first blithely proclaimed my intentions I really did think I wanted to be the oldest man in the world. It may sound peculiarly childish, but I liked the idea of getting a letter from the Queen, of living for a whole century, of being alive longer than anybody else. I also thought I had a good chance. Walter Breuning is the world's current oldest man, with 113 years to his name. That doesn't sound too far off. I'm fairly careful, I thought. I don't smoke, I rarely shave, and I'm not allergic to peanuts. I could do it.

But the more research I did, the tougher the challenge seemed. It wouldn't just be a case of sitting in a soft environment, playing the waiting game; it would be raw survival. It's a dangerous world out there. Could I really cheat death till I was 120? And what if I did get what I wished for? What if I did live until the year 2100? Would that really be fun, let alone funny?

Unsurprisingly, perhaps, our sentient species is obsessed with the idea of staying alive. Every day numerous articles are published proclaiming the secret to longevity. "Never sleep more than seven hours a night," warns one journal; "Ten hours' sleep per night guarantees a long life," insists another. Recent tips include making as many female friends as possible, eating huge amounts of wheat, and drinking one glass of red wine every day. It does sound quite fun. But every proper scientist in the lucrative field seems to agree that provided you live a healthy life, it's your genes that really count.

This is good news for me. I have three grandparents still going fairly strong today, and my mum and dad are positively robust. So to find out what life is actually like when you've been around for a century or so, I went to visit some of my more advanced relatives, as well as a couple of people even higher up the Oldest Person In The World leaderboard.

Joan is my great aunt. She's my mum's mother's sister and she'll be 93 in November. I hadn't been to her house in Worthing since I was a boy, some 25 years ago, but she welcomed me with a pot of coffee, happy to talk about her life. She gave me the good news first, with some biscuits: her Aunt Maud had lived to 100 and her Aunt Tat had made it to 101 and a half. Her maternal grandfather lived to 91 and her great grandfather was 87 when he passed away. "Our constitution is sturdy," she told me. Great genes, I muttered to myself.

Joan herself looks like she'd have no trouble passing the three-figure mark, and I asked her how she'd stayed so fit. "I've always had something to do," she said. "I keep my brain and body active with needlework, crosswords, Sudokus or duplicate bridge." Joan is a five-star master of the latter, and it was clear she's still fiercely competitive. "I'm the oldest member of the club," she said proudly, "after Alan, who's 96 and an ex-international. I garden like mad too. And I cycled until recently."

When the biscuits were finished I told Joan about my own plan to live a long life. She shook her head. "You're unlucky," she sighed, "because you live in this awful age of technology. Most people nowadays just sit in front of the TV in their flat, then take the lift down to their car. They don't use their bloody legs. That's why everyone has wonky hips and knees." I glanced down at my legs. They did look quite wonky. I made a mental note to go for my second jog of the year soon.

Since Gordon, her husband, died in 1980, Joan has lived alone in her immaculate four-bedroom house. During a brisk stroll around her one-acre garden ("the last bit of wild in Worthing") I asked if she was enjoying her 10th decade. "No. No. Not in the slightest," she said, smiling and catching me by surprise. "Don't get old – it's terribly boring. I hated being 70, I hated being 80, and I hate the loss of my physical strength. My mind is just the same as it's always been, so I feel very frustrated." So you're not interested in getting to 100? "Oh no, no, no. I just hope I don't linger. I'd prefer to die in my garden than to go into hospital," she replied firmly.

Our chat was inspiring but sobering. Joan is an impressive lady, positive but realistic, reflective but practical. "Old age is awfully difficult to explain," she said just before I left. "But you just have to bloody well endure it and remember those who are so much worse than you." Becoming the World's Oldest Man would clearly be no walk in the park.

According to statistics from the United Nations, I can expect to live for 77 years as a UK resident. We're placed 25th in the world rankings, just better than Germany (for once) and a long way behind the Japanese, who at number one can expect to live to 82.6 years old. But even in this country there are now more than 10,000 people alive aged 100 or more. When these people were born, there were just 100 people in England and Wales who had reached that milestone. Diet, healthcare and general living standards have all improved to such an extent that our life expectancy has doubled in the past 200 years. But instead of being a cause for celebration, this increasingly elderly population is a worry. On a national scale, more money than ever is needed to pay for their healthcare, pensions and other social needs. On a personal level, more families are finding themselves unable to look after aged relatives who are unable to look after themselves. My great aunt Joan is unusual in her independence. If I do become the Oldest Man In The World, I'll almost certainly have to mark the occasion in some sort of institution. Is that what I want? Will I have any choice?

I drove to Faringdon in Oxfordshire to meet George. He'd recently celebrated his 100th birthday in a care home called Ferendune Court, and I was excited to meet my first centenarian. But as soon as I joined him in the dining room it was clear he was rather less impressed by me. As he polished off a generous portion of kippers, I sat awkwardly beside him. I didn't want to stare, but this was the oldest man I'd ever met, dressed neatly in shirt and tie, hair thick and tidy, eyes bright. I tried to introduce myself a couple of times but George was paying far more attention to his breakfast.

Thinking his hearing might be the problem, I tried raising my voice. "I'm Alex," I barked. "I've come to talk to you because you're 100 years old." Just as I was about to try bellowing, a kindly nurse stepped in. "This is Alex," she said, far more calmly. "He's from the newspaper." "He's not a doctor then," said George, clearly relieved. "No, he just wants to talk about your life." Although George couldn't understand why anyone would just want to talk to him about his life, he was happy to answer my questions, so long as I didn't prod his kidneys. "I had a bit of pain last week," he told me conspiratorially, "but I'm fine really."

"I'm fine really" and "I'm nothing special" were George's key phrases. I asked him where he grew up, what he did for a living and how he'd managed to live so long, and every answer ended with one or the other. I learned that he'd worked on a farm, played in a band with the scouts and had always enjoyed a hearty breakfast, but all his replies were poignantly humble. I asked him if he was pleased to get a letter from the Queen on his 100th birthday and he said he wasn't interested in all that. "The trouble with living so long," he said, after the longest pause yet, "is that all your contemporaries die first."

It emerged that George was still coming to terms with yet another recent loss. "I do still muck about here sometimes," he said, but I wasn't sure how often that might be. I may have met him on a difficult day, but there was no denying it: George seemed sad to be 100. Even though this was another blow to my own ridiculous plan, I was ashamed to feel a rush of relief when I left him; I was still young, still able to jump back into my car and race away from his final home.

I'd grown accustomed to this guilt in the course of visiting my own grandparents over the past few years. Recent trips to see them have rarely been joyful occasions. But I wanted to ask them outright how they felt about old age so first dropped into my grandfather's nursing home in Worthing. As always, I felt uneasy as I walked down the corridor to his room, fully aware that he might well sleep through my visit or, if awake, make little sense. Since he had a stroke six years ago, his mind has become increasingly liberated from reality and he has been known to insist that he is both 150 years old and, yes, the oldest man in the world. He's really 91.

Through his open door I could see that he was fast asleep. I tried, gently, to wake him, standing self-consciously at the side of his bed, calling: "Grandpa, it's Alex" at ever longer intervals, but he wouldn't stir. The nurses had advised me to tickle his ear if I wanted to rouse him but he looked so peaceful it didn't seem fair to disturb him, especially like that. But eventually, feeling very much like a character in The BFG, I did tickle the large earlobe of my grandfather and he opened his eyes.

"Who's that?" he said. He is no longer able to see more than dim shapes. I told him I was his second eldest grandson. "Alex? Good Lord! Is Rachel with you, and the boy?" "No, it's just me, Grandpa." "Well, good Lord. What a wonderful surprise! I can't offer you anything I'm afraid, old boy. I've got absolutely nothing in."

I'd picked a good day. I was pleased he'd remembered me and my family and relieved he didn't mind the tickling so got straight to the point and asked him what it's like to be his age. "It's not good, to be honest," he replied briskly. "You really need to die when there are still people around who knew you when you were yourself. The ones who are left now are just guessing. It's much better that you die at the same time as your friends."

"Right," I said, taken aback by his honesty. At least George wasn't alone on this one. I asked him why he thought he'd lived longer than his friends and he thought for a while before saying softly: "One never does know. I don't even know if I'm lucky or unlucky to have lived so long. I always thought that it would be a wonderful thing to live for a long time, but I'm not so sure now, because everyone's gone."

Although a little wistful, Grandpa didn't seem overly upset by this state of affairs. In fact, he soon adopted a positively upbeat tone, telling me how I should break the record. "You don't need to worry too much, Alex," he told me. "If you're able not to worry too much, that will help you. If you're able to accept that life is for living, then all you do is live as well as you can, behave yourself, be fair to other people, and hope for the best. That's all you can do. And you might as well have fun because you never know, you might die tomorrow." I hadn't seen him as lucid as this for months. He seemed perked up by this all-too-rare chance to impart some more wisdom to a grandchild. And he was quite right, of course. Perhaps I shouldn't spend too long fretting about my long life and actually live it.

Our conversation did inevitably feature some moments of spectacular misfiring on Grandpa's part. When I asked him his current age he insisted that he was one year old. He almost certainly meant 100 years, but it seemed fitting that he'd chosen the same age as my son. As I spoke to him slowly with simple words, helped him sip water from a beaker and tucked the blanket under his chin when he felt cold, the cyclical nature of life had never seemed more apparent. But again, this aspect of old age seemed natural, not depressing. He was content to spend nearly all his time in bed now. He was comfortable. "I sleep well because I'm happy with my life. I think to myself how fortunate I am. People look after me here. Sometimes they ignore me, but they're quite right to. I don't need anything now. I just go to sleep. And the Good Lord Above will say, 'That's enough' when I've had enough."

"So you haven't had enough yet, Grandpa?"

"I don't know, old boy. I thought I might have, but then you came and asked me all those questions." And with that, his eyelids began to droop again. I held his hand and said goodbye. "Goodbye then. Is that your hand? It feels very big compared to mine."

His wife, my grandmother, lives in a different care home, closer to my parents, and although her short-term memory is incredibly poor and her body frail and stooped, she's far more healthy and mobile than Grandpa. But while he is happily bedridden, Nana is utterly frustrated by her situation. When I arrived her face lit up. "Oh, I'm so glad you've come to see me!" she cried. "I've been ever so lonely!" I knew from the signing-in book that she'd already had two visitors that morning.

Nana is 84 years old and I asked her if she fancied living another 16 years. "Oh no, dear," she said without a pause. "I find life very difficult now because whatever I try to do, I feel I'm just marking time. I find it difficult trying to be jolly all the time. But it's silly, really, because I'm so fortunate to be as fit as I am. I'm so glad you've come to see me." Once more, my comical record attempt seemed rather less amusing.

My grandmother repeats herself a lot nowadays and conversations tend not to last long before stopping and starting again. I asked her if she was enjoying her 80s. "Not greatly," she said. "It's possibly my own fault, but I've found it difficult to adjust and to integrate. Time goes very slowly here. Sometimes it feels right; often it doesn't. I'm so glad you've come to see me."

In truth I already knew that Nana hated being old, so instead of reminding her with more questions, I told her about her great-grandson and we talked about the weather until it was time for me to leave. When she asked me not to go I felt the usual guilt, followed by relief when I was back in my car. I know both she and Grandpa are in great care homes, but it's impossible not to feel slightly uncaring leaving them there. Would I want to be left there? Probably not. But would I want my children worrying about me all the time? Definitely not. So is it possible to be happy and 100? I had to hope so.

Since 1840 the highest average life expectancy in the world has risen by three months every year. If this rate continues, people in Japan would live on average to 100 in just 60 years' time. In other words, centenarians like George will be commonplace by the time I'm his age.

Jeanne Calment, the official oldest person ever, lived to be 122 years and 164 days, although authorities in the former Soviet Republic of Georgia have claimed that a mountain lady called Antisa Khvichava has just turned 130 (the Gerontology Research Group has yet to examine the evidence). There have been many rumours of people living enormously long lives throughout history. Epimenides of Crete was said to have lived for 290 years, starting in the 7th century BC, and according to the Old Testament, Noah lived to be 950 years old and Methuselah 969. As absurd as this may sound, Dr Aubrey de Grey, editor-in-chief of the journal Rejuvenation Research and author of the books The Mitochondrial Free Radical Theory of Aging and Ending Aging, believes that we could all soon be able to live to 1,000.

According to the Cambridge-educated scientist, the fundamental knowledge needed to develop effective anti-ageing medicine already exists. He argues that the seven biochemical processes that cause the damage which accumulates during old age have been discovered, and if we can counter them we can, in theory at least, halt the ageing process. If he's right – and admittedly that is quite a big "if" – then this record attempt of mine could last well into the next millennium. But even if he's wrong, the evidence still points to there being many more extremely old people around in the future.

I'd never heard the word "supercentenarian" before I met one. Ellen Watson is 110 years old and thus qualifies for the heroic title. She lives in Meadowside Nursing Home in Staines and was the last person I'd arranged to visit. After my previous encounters I was especially nervous about this one. By now I'd learned that great age was not necessarily great fun. It was no barrel of laughs. But I needn't have worried. Ellen had other ideas.

Born on 3 January 1900, Ellen is the very first person to be born in the 20th century still alive today, and having recently broken into the Top 10 of the oldest people in the UK charts, she's now, finally, something of a celebrity. I was certainly not the first journalist to come to see her but she insisted on dressing up for the occasion, wearing a bright pink dress and a bright pink hat. "I look like I'm going to Ascot," she said as soon as we met. Then she laughed.

From the moment I'd walked into her Anchor Trust care home it had felt different. There was music playing – loudly, not in the background; the walls were covered in photos and personal pictures instead of the usual generic watercolours, and Sally, the lady who would look after me for the afternoon, couldn't have been more excited to see me. She couldn't wait to introduce me to her friend Ellen.

"Here he is!" she shouted, ushering me into the lounge where the eighth oldest person in the UK sat, flanked by six other grinning ladies. She knelt down beside Ellen and shouted in her ear: "And he wants to know what it feels like to be 110!" This was the way my interview would work. Sally would fire my questions to Ellen at very close range and Ellen would take her time, then reply succinctly.

"It feels good to be 110," she told me, "but I don't know how it happened. I'm just pleased it did." She told me she still walks around the home, she even dances on occasion, and she still plays bingo ("I wish I won more"). She still looks forward to her little pleasures but she doesn't see anything unusual about that. "You have bacon and eggs every morning too, don't you, Ellen?" asked Sally. "Is that your secret?" "No," replied Ellen, and laughed again.

I almost got the impression that Ellen really did know the secret to long life but wasn't going to share it just yet. She had such a sparkle about her that anything seemed possible. She sang and we clapped. She joked and we laughed. "You became a great-great-great-grandmother last week," shouted Sally. "I know!" Ellen shouted back, feigning impatience, still able to tease at 110.

She showed me the cards the Queen had sent her over the past decade and told me how disappointed she was that the monarch hadn't changed her outfit for the last few. I didn't know she sent a card every year after you pass the 105 mark, but then not a lot of people live that long. There have only ever been 106 verified supercentenarians in the UK.

Through Sally I asked Ellen if she thought she'd make it to 111. "Yeah, I expect so," she said, like a teenager. In fact I wouldn't be at all surprised if she becomes a teenager again two years after that. "And do you like all the attention?" "Absolutely!" she replied and reached for another slice of the cake they'd ordered specially for my visit.

At last I'd found somebody who was enjoying being older than everyone else. Perhaps it was because she'd got through the tricky 80s, 90s and 100s, and was now able to bask in her top 10 status, but even without the title of supercentenarian I'm sure Ellen would be cheerful. As Sally repeatedly told me, she is a star.

In the search for longevity it seemed to me that this steadfastly bright disposition was even more important than good genes. You can't live to 110 without some tragedy in your life, some hardship, much loss. But Ellen proved to me that you can still look forward. You can still enjoy life. When I finally, reluctantly, got up to go she kissed my hand and I blushed. I told her it was a pleasure to meet her. She laughed and shouted: "He's a nice man!" to her friends. I'm pretty sure she winked at them, too. When she turns 111 in January next year she said I could come to the party. I can't wait.

As for my own world record attempt, it's still on. After all, as Grandpa told me, life is for living.

How to cheat death

1) Eat some things, don't eat others The good news is that the Erasmus University in Rotterdam recommends consuming garlic, vegetables, fruits, almonds, dark chocolate and wine every day to extend your life expectancy by 6.6 years. The bad news is that, according to the Loma Linda University in California, you can live 3.6 years longer by eating meat less than once a week.

2) Move to Japan (or Eastbourne) Residents of Japan live longer than anyone anywhere else in the world. But if that's too much of a commute, try Eastbourne. The University of Sheffield has reported that life expectancy there is 6.2 years higher than the national average.

3) Believe Another study, this time by the University of Pittsburgh, claims that those who go to weekly religious services live on average three years longer than those who don't. The University of Manchester, meanwhile, announced last month that Methodists live seven years longer than the rest of the population, with female Methodists dying at an average age of 91.1.

4) Marry someone who makes you smile The Norwich Union has also dabbled in longevity research and claims that people who are married or who live with a partner can expect to live a year longer than those who don't. Back over in America, researchers at Wayne State University in Michigan studied old photos of baseball players and discovered that those who smiled for the camera lived seven years longer than the non-smilers.

5) Floss your teeth The gerontologist Dr Michael Roizen claims that flossing your teeth every day can add six years to your life. The bacteria that cause gum disease can linger in your arteries, causing inflammation which in turn can cause heart disease. So you might as well floss.

6) Don't sit down That's right: sitting down is bad for you. The American Cancer Society analysed death rates and activity levels of more than 123,000 healthy men and women for 13 years and discovered that men who spent more than six hours of leisure time a day sitting had a 20% increased risk of death. Women who spent their free time watching television, reading, or basically not standing were 40% more likely to die than those who were on their feet. Are you reading this on a chair?

Alex Horne is a comedian and writer. His new show, Odds, runs at the Pleasance Upstairs in Edinburgh until 30 August (alexhorne.com)