Like a lot of people who are getting on, I find myself wondering about my brain. If I mislay my glasses, or struggle with a name, is it just common-or-garden forgetfulness – the sort of slip I might have made well before hitting 60 – or something more worrying?

Why, I think, did I have to ask my wife to remind me what we’re doing for her birthday? Why can’t I remember if I locked the front door? Why did I fail to send that email I desperately need an answer to?

I don’t immediately think dementia. But look, I’ve written the word, and there’s no denying it’s at the back of my mind. There are close to a million people living with the condition in the UK; around 6m in the US; tens of millions more across China, India, Finland, Australia, Azerbaijan … My mother watched her best friend get it, then developed it herself. Everyone knows someone who has or had it.

Then there’s mild cognitive impairment (MCI), sometimes known as cognitive decline, which can make it hard to focus, to remember and learn things, to reason or to find the right words. The best you can say about MCI is that there is no guarantee it will end in dementia – which normally involves a buildup of proteins in the brain and/or a restricted blood supply, possibly as a result of a stroke.

MCI does not always get worse; sometimes it can even be reversed, since the causes include sleep disorders, low blood pressure, hearing loss and severe constipation.

You’ll need to see a doctor to be diagnosed with MCI, but some of the descriptions sound all too relatable. “People with MCI often have difficulties remembering things as well as they once did,” says the Alzheimer’s Society website. “Others describe more of a ‘brain fog’ where they feel unable to think clearly.”

I’d rather not be thinking about this on a day when I have woken up stone-cold sober but feeling as if I had been drinking all night. I’ve already forgotten the keys I needed for work and almost missed an appointment because I got on the wrong train.

Still, I have finally made it to the Aston Brain Centre in Birmingham, where, as part of my quest to live to 100, I am due to stick my head in a giant metal helmet that looks a lot like an old-fashioned salon hairdryer. “Meg” – officially an MEG or magnetoencephalography scanner – is used to measure the magnetic fields produced by electrical activity in the brain. The contraption is so sensitive that she sits in a shielded room and visitors must remove anything metallic, from rings to watches to belts. I’ve got a crown on one of my molars, and while I can’t take it out, I have to declare it so the expert who will analyse my brain patterns can make allowances.

Meg is mostly used to study childhood epilepsy, dyslexia, autism and attention deficit hyperactivity disorder, but for a few hours every week she’s taken over by a company called MYndspan, which examines the brains of the worried well like me, as well as patients recovering from head injuries and athletes involved in contact sports. A first-time scan will set you back £600, but you can see why it would appeal to a professional boxer or rugby player, regularly risking concussion or worse. It won’t tell you everything you may want to know about the structure of your brain – for that you’d probably want an MRI or a CT scan – but it will provide a snapshot of its functioning. MYndspan describes the initial scan as the “baseline assessment” against which you can measure any future changes.

I’ll get into the scanner in a minute, but first they want some basic information about my medical history and lifestyle – especially as regards nutrition, sleep and exercise. Caitlin Baltzer, MYndspan’s CEO, calls these the “three pillars of brain health”. Then come what she describes as “gamified cognitive assessments”, which measure things like short-term working memory, attention span and spatial skill. There’s a lot of matching shapes on an iPad screen, a lot of “What was under this tile the last time you clicked it?” and a lot of true-or-false questions, all against the clock. I think I do well on the word games and the “Is this sketch on the left exactly the same as that sketch on the right?” bit but overall I have no idea how I score. The 20 or so minutes it all takes feels too short and too long. “How can you judge a mind so quickly?” I think, but also: “Make this stop!” The longer it goes on, the more likely it is I will screw up.

The same goes for the scan itself. Sian Worthen, who manages Meg for the Brain Centre, attaches a few wires to me, uses a digital pen to fine-tune a 3D model of my head, then settles me into my seat and slowly lowers Meg’s hood until it touches the top of my scalp, blocking most of my vision. A cross appears on a screen in front of me, the lights dim, and Worthen leaves the room and shuts the door. Through a loudspeaker, she asks me to look right, left, up, down, clench my teeth, take a few deep breaths and shut my eyes. This will help her adjust for the changes caused by even small movements. Then it’s time to stare at the cross, blinking as little as possible and trying not to look away. I must not fall asleep, even though I am tired, it’s a warm day and there’s none of the clanging and banging you get with an a MRI.

It’s harder than you’d imagine. What starts out as a single pure-white cross sprouts coloured fringes, then suddenly there are two crosses, which merge and separate and blur and come back into focus. Two or three times I shut my eyes, then snap them open fretting that I have dozed off. I start counting seconds, trying to work out how long I’ve been in here and, at about 300, Worthen announces that we’ve reached halfway. Somehow I barely manage 150 in the next five minutes. It makes me wonder what the test is going to reveal, if I’m struggling with counting or the passage of time.

Back home, waiting for the results, I take a couple of other online cognition tests, from the brain injury therapist Natalie Mackenzie and the Food for the Brain Foundation, the second based on the assessment used in NHS memory clinics. There’s no scanning this time, just more screen-based games and questions about my lifestyle and health. They’re both longer than MYndspan’s, with Food for the Brain’s focusing much more on diet. Patrick Holford, the charity’s founder, is keen to stress the role of B vitamins, vitamin D and omega-3 fatty acids in preventing dementia. I flounder a little with some of the questions. Was it B6 or B12 I started taking a few months ago? No, I’m pretty sure it was vitamin D. Did I mention I have trouble remembering things?

Anyway, what’s the verdict?

First, MYndspan. There’s no way to say this without sounding insufferably smug, but I have a remarkably youthful brain. Based on the results from Meg, its “functional” age is 45.2 years – a decade and a half less than its chronological age. This is as encouraging as it sounds, according to Ben Dunkley, MYndspan’s chief science officer. Physical damage can make a brain appear younger, he says, “but I think in your case, with no history of brain injury and things like that, this is a good measure”. As for my overall cognition, as measured by those iPad games and ranked against other men aged 55 to 64, I am “within the average range”, apart from two areas in which I am “exceptional” – concentration and grammatical ability. Nothing, I am pleased to see, is below average.

It’s a similar story from Natalie Mackenzie: “average” in 11 areas, “above average” in one – grammatical or verbal reasoning. “Common everyday activities associated with verbal reasoning,” I learn, include “texting a clear description of an item to your partner so they can pick it up from the grocery store”. It’s nice to know who’s to blame when there’s no milk in the fridge.

Food for the Brain, meanwhile, scores my cognitive function at 80.87, versus an expected average of 54.2. “You performed at or above the norm for your age,” it explains. “This suggests that you are not showing the early cognitive function problems that can be a symptom of future cognitive impairment and Alzheimer’s disease.” Those are my italics, but I’m not apologising for them.

“It’s a very good score for your age,” Holford confirms. This test, which has been taken by more than 400,000 people, does have limitations – it’s not great for anyone with dyslexia or autism, for example – but it is more likely to understate cognitive function than to exaggerate it.

There’s more good news from my dementia risk rating. “About 89% of dementia is, in our opinion, largely preventable,” Holford says.

That’s a message that’s often forgotten. It certainly keeps slipping my mind. “Dementia is not a natural part of ageing,” the Alzheimer’s Society reminds us. Even over 80 there’s just a one in six chance of developing dementia, according to the nursing charity Dementia UK.

Food for the Brain lists eight risk factors that are at least partly controllable – everything from diet to sleep and activity levels – and scores each from green (low) to red (high), via yellow (small) and orange (significant). Five of my factors are green; the remainder are yellow. “It’s showing you a few areas with room for improvement,” says Holford, who has just launched a tool called Cognition to nudge users to change their behaviour. Like MYndspan, Food for the Brain encourages you to test yourself regularly so you can spot any changes.

It sometimes feels like the only way to escape dementia is a pre-emptive death. It’s good to be reminded that not only do most people sidestep it, but you can improve your odds of doing so. “There’s no certain way to prevent all types of dementia,” the NHS says. However, research suggests that “by modifying the risk factors we are able to change, around four in 10 cases of dementia could be prevented”.

How? We need to stay stimulated and mentally engaged, whether that’s by socialising, or looking after our mental health, or simply making sure that if we need a hearing aid, we get one. We need to avoid blows to the head. And then there’s a whole slew of actions that the NHS sums up as: what’s good for your heart is also good for your brain. “This means you can help reduce your risk of dementia by: eating a balanced diet; maintaining a healthy weight; exercising regularly; keeping alcohol within recommended limits; stopping smoking; keeping your blood pressure at a healthy level.”

In other words, almost everything we know we should be doing for the sake of our bodies, from choosing salad over chips, to walking to work rather than jumping on the bus, will also protect our minds. As Holford puts it: “The first myth to dispel about dementia is that you’re guaranteed to get it.”