There’s no getting away from it: I come across as smug. In March, kicking off what I hope will be a very long series of articles, I wrote that I was in “great shape” for a 60-year-old, with plans to make it to 100. I ran 30-40km every week, I added, on top of yoga and high-intensity interval training. In April I celebrated my “freakishly strong” core; in May my “remarkably youthful” brain. And that’s just what I put in writing. At home, I can barely pass a mirror without pulling up my shirt to admire the faint beginnings of a six-pack. When I’m running and I overtake someone decades younger, I get such a bounce in my step that even I think I deserve a slap.

But here’s the thing: what’s mostly going through my mind is not: “I’m amazing!” but: “I’m amazed!” For three-quarters of my life there was nothing to suggest I might ever get into shape. I don’t come from a sporty family, and as for school (with its rugby, cricket, football, gymnastics, swimming, etc) I remember precisely one game that I played rather than endured: a hockey match at 14 or 15, when I was in goal and, for once, found myself blocking shot after shot instead of watching them whiz into the net. This was the only time any of my teammates looked at me with something other than sympathy or scorn.

Other than that, it was afternoon after afternoon of standing around bored, or running around uncomfortably, or being yelled at by an angry adult who had once dreamed of becoming a professional athlete.

I’m not saying I was traumatised, but I definitely wasn’t inspired. Over the next three decades, vaguely aware I should do something to look after my body, I had brief flirtations with rowing, swimming, cycling and kayaking, but mostly I concentrated on eating, drinking and sitting my way into an early grave.

By the late 2000s, as I wrote at the time: “Not only was I clinically obese; I was in denial. I had broken a neighbour’s bench just by sitting on it. My mother would nod at my stomach and ask when ‘it’ was due. One so-called friend shouted ‘Thar he blows!’ when I joined him on a beach. I told myself I just needed to lose a few pounds, and it was normal for my thighs to rub holes in my jeans.” My cholesterol was far too high, and when I was on edge or miserable, the only remedy I knew was to open another bottle. And there always was another bottle. I was living in France, so even good wine was cheap – and I had a cellar.

I was 45 before I made a real effort to improve my diet, 50 before I started the NHS’s “Couch to 5k” plan and discovered that running could structure my attempt to reshape myself; and 57 before I finally gave up booze. There was a lot of slippage on the way, but in my – no, seriously? – seventh decade it feels as if I’ve settled into a healthy relationship with my own body. And I think I’ve learned a few things worth sharing with other late starters.

Just because you loathed PE, you will not necessarily hate all physical activity.

This time there won’t be some blowhard whistling at you, or a supposed friend who would rather die than have you on his team. Now, you can choose how hard you push yourself, how long you spend doing it, and whether or not you do it when it’s raining, when you’re on your period, or when you just woke up aching.

That said, don’t count on any kind of transcendental experience.

It took me years of running before I got anything like a high.

But don’t write off the possibility either.

Last week’s yoga class was coming to an end, we were lying with our eyes closed in “corpse” pose and the instructor began massaging my temples with essential oil. I felt like a cat does when you rub it behind the ears.

Don’t underestimate the power (and pleasure) of walking.

It will shift weight (if that’s what you’re after), condition you for something more strenuous and give you space to think or listen to your favourite music or podcast. Although most of the world seems to have forgotten this, it will also get you places – and more reliably than any other form of transport. Your feet will never go on strike, get stuck in a jam or be held at a station while an engineer arrives to reset the emergency alarm.

Start with something you may enjoy, not something that friends or experts swear is good for you.

Your starter exercise does not have to provide an all-body workout or stretch your mind as well as your muscles. Your priority should be to get moving, and become comfortable with your body so you can branch out when you need to. Which you will, because …

Even if cardio is your thing, you can’t ignore resistance work.

The older we get, the more muscle we lose, making it more likely that we will “have a fall” – and struggle to recover from it. To build it back, you will have to lift weights, learn how to use those frightening machines in the gym, or leverage the weight of your own body with push-ups, planks, lunges and squats.

Even if resistance work is your thing, you can’t ignore cardio.

For a long, active life you need to stretch your heart, lungs and circulation as well as your abs, glutes and traps.

This world is nothing but hills!

You’ll just have to suck this up once you start running, cycling or even walking seriously. Living at the bottom of a long, steep slope, I’m reconciled to starting most runs with a six-minute climb. There are lovely parks at the end of it, and a nature reserve, and more bloody hills.

Sweating like a pig doesn’t mean you’re unfit.

Sample size of one here, so it’s not exactly scientific, but I still get red and drippy as soon as my pulse is raised. If I’m exercising outdoors, I’m happiest in drizzle; if I’m doing hot yoga, with the room at 37C, there are puddles of brine around me. Sorry, yoga-mates. But also, if we’re 15 minutes in and you’re not even glowing, I hate you.

If you’re not enjoying yourself, try to narrow down why.

Is it the activity that’s rubbing you up the wrong way, or the environment? If you’re swimming, you may discover that you hate pools but love open water. If you’re running, you may far prefer roads, the treadmill or forest trails – with or without company, or music, or a target time and pace.

When you exercise matters – just not in the way that most people say it does.

Maybe you work out best at 6am on an empty stomach, a few hours later when you’ve had breakfast and given it time to settle, or even late at night. Whatever you choose, someone on the internet will tell you that you’re doing it all wrong for maximum gains, and have the scientific studies to prove it. Tell them to get stuffed. They’re talking about average or typical humans. You are you; you do you.

You will rarely regret paying for an instructor or personal trainer. Gyms, however …

If you find a trainer or teacher that you click with, and can afford a few classes, it will do wonders for your confidence and technique. When it comes to gyms, however, investing money in a membership is no guarantee you will invest time and effort. Do not sign a long-term contract unless you are 100% sure it is right for you.

If you’re still working, your company may have arranged what looks like a fantastic 12-month deal with a local gym – but will you have time to use it in your lunch break, or the inclination to visit before or after work? Do you really want to be wiping your thigh-sweat off the hip adductor machine so your boss can use it after you? Come to think of it, do you even like being in a gym?

You will move better if your hands are empty.

If you really can’t run without your mobile phone or water bottle, get a belt, armband or a backpack that will hold it. Some shorts and leggings even have things called pockets.

If it’s hurting, stop it.

A little soreness is usually fine, especially after you’ve exercised. If all you have to worry about is blisters, the squishy, expensive “healing” plasters are worth every penny. But don’t ignore anything stabbing, grinding, shooting or knee-buckling. Stop what you’re doing and take at least a week off. If you feel confident about resuming without seeing a doctor, physio (etc), start slowly and be prepared to stop again.

In fact, if you’re hating it, stop it.

Sometimes a workout just doesn’t work out – you’re more tired than you thought, or you can’t focus, or you are unexpectedly hating every minute. Give yourself a little longer; then, if you’re sure this isn’t something you can push through, cut the session short and tell yourself you’re making sure you’re in better shape for next time. Particularly at the start, you’re training your brain as much as your body. Try not to teach it that exercise is horrible.

That said, the ‘second wind’ really is a thing.

I often find myself struggling for the first 6km of a run, then finally hit my stride. I don’t pretend to understand why.

Don’t expect exercise alone to fix your body.

It’s part of the puzzle, but how you eat and feel and sleep are equally important. Also …

If you’ve got a monkey on your back, maybe give it a little shake every now and again to see if it will let go.

All the push-ups, pilates and ping-pong in the world won’t make up for a problem with drink, drugs or nicotine. I have no first-hand experience of the last two. All I know is that sometimes you can outlast what seemed like an integral part of life. In 2020, at least 40 years after my first ever alcoholic drink, I had what I hope and expect will be my last. It was the first time I’d managed to give up for more than a few weeks. By the time of that final glass, I was drinking at least a bottle of wine most nights. I have no idea how I stopped this time, or why I have since felt nothing more than mild longing for a mouthful of red when I am cooking. Maybe I was just ready? Maybe it was time? My drinking was never purely about stress, but it must have helped that exercise gave me another way to cope.

If you’re fit enough to exercise with young people, go for it.

Sure, you’re old enough to be everyone’s father. But no one is looking at you – not with that wrinkly skin. Or, if they are, it’s because they’re so impressed with your side plank. You, meanwhile, are being pushed a bit harder than you would with a bunch of over-55s.

Embrace the cheerleaders, ignore the others.

Someone, somewhere is aching to tell you that you’re wasting your time, or even heading for a heart attack. Try to remember you’re doing this for you, not for some idiot who never got over the fact that the man who popularised jogging died while – oh, my aching sides! – jogging. The last bloke who gave me some “friendly” advice was about my age and looked 20 years older. He was selling flowers outside a cemetery, which I guess was some kind of message.

You should probably try yoga.

Leaving aside what it does for flexibility and balance, there’s something about it that chips away at your cynicism. I started out curling my lip at the “third eye” and the talk of gratitude; now I can bow my head and namaste with the best of them. If you’re a yogi looking for a slogan, could I suggest: “I can sweeten even the sourest old fart”?

If you’re on a long run or cycle ride, make sure you know where the toilets are.

Especially first thing in the morning – once you get your body moving, your bowels will also spring into action.

Lifting a few dumbbells will not suddenly turn you into another Arnie.

Even Schwarzenegger had to work incredibly hard at it. This is either very good news or very bad, depending on your #fitnessgoals.

You’ll change your taste in music.

One minute you’re listening to the Smiths and the KLF, the next it’s all Dua Lipa and Rihanna. Blame those exercise classes with their poppy earworms, and the fact that it’s more enjoyable to run to RiRi’s We Found Love than Morrissey singing Meat Is Murder.

There may come a point where you no longer recognise yourself.

My wife, who has also worked hard on her fitness, often jokes that the Phil and Hannah of 10 years ago would despise the Phil and Hannah of today. “What a couple of tossers,” she said the other night, as we headed off to a class together. But that says more about the old us than the new.

• This article was amended on 5 June 2024 to add information about the fourth embedded image which features a sculpture by Richard Trupp called The Juggernaut of Nought.