It is one of the ultimate questions that scientists have been wrestling with for decades: how can we predict how long someone will live?

And when people naturally look younger than their years, or live to 100, what is their secret? Is it written in their DNA, just good luck, or can we learn something from their lifestyles to boost our own health and lifespan, as well as our looks?

It’s a fascinating argument among the growing number of experts working in longevity science – the field of healthy ageing.

For years, studies have analysed huge numbers of people – including so-called ‘super-agers’ who live remarkably long and healthy lives – to examine the factors that influence ageing. It’s tempting to conclude that it is largely out of our control, and that the genes we inherit dictate how long we’ll live.

But the evidence suggests something rather surprising: namely that our genetic make-up, which dictates everything from eye colour to susceptibility to disease, actually contributes an effect of only about 20 per cent.

Lifestyle – diet and exercise, in other words – is considered overwhelmingly more important.

Studies also suggest that if you look at least five years younger than your actual age, you may be less at risk of some of the most common conditions of ageing, from bone-thinning disease osteoporosis to lung disease, hearing loss and cataracts.

Youthful looks have also been associated with better thinking and memory skills.

Chrissie Turner, 80, from Eastrea, Cambridgeshire, has now outlived all of her family 

Barry Squance, 76, a retired chiropodist from Wells, Somerset, plays golf and goes walking and cycling

Gillie Coghlan, 72, lives in the Cotswolds and is highly active

To test this out, The Mail on Sunday’s resident GP columnist, Dr Ellie Cannon, asked readers to get in touch if they believed they looked younger than their years.

Dozens aged between 62 and 90 wrote in with photographic evidence, and we spoke to three, who all look more youthful than their passport suggests. And taken together, their experiences paint an intriguing picture of the factors that influence healthier ageing.

All, for example, cook from scratch and avoid heavily processed foods. None are meaningfully overweight or have serious health conditions, and none smoke or drink heavily.

In every case they lead fulfilling and sociable lives, with wide circles of friends. Most get regular exercise or at least stay active. Certainly none of them see their advancing age as a barrier to living their lives fully, and all view the world through a positive, optimistic lens.

And while some have parents or grandparents who lived into their 90s and beyond, others have succeeded in reaching an older age despite losing parents and siblings significantly earlier.

It means, perhaps, that we could all learn a little from them.

As 76-year-old self-confessed ‘eternal optimist’ Barry Squance put it: ‘I never take life for granted, but grasp it with both hands and live it to the utmost.’

And another, Gillie Coghlan, 72, who had been at a gig and got home at 2am the night before our interview, said: ‘Nothing scares me more than a routine or settling down. I’m me for ever – my age is completely irrelevant.’

It’s positive, too, that the main message from experts is that it is never too late to make changes which could not only extend your life, but could give you more years of good health.

Professor Ilaria Bellantuono, co-director of the Healthy Lifespan Institute at the University of Sheffield, says: ‘There are various studies which tell us different things about the extent of the role genetics plays in how well we age.

‘If you look younger, it may be a marker for whatever else is going on in your body. Certainly it likely means you are healthy, your muscles may be in better shape and you don’t have premature wrinkles from smoking or other unhealthy behaviours.

‘But it’s never too late to start being healthy. You can slow it down, or you can accelerate it, depending on what you do.’

Much of what experts understand about ageing well comes from the so-called Blue Zones – geographical areas such as Sardinia in Italy and Okinawa in Japan where people live, on average, the longest and healthiest lives in the world, often surpassing 100.

That’s significantly more than the average life expectancy in the UK, which is 79.1 for men and 83 for women.

Those living in these communities share key characteristics. For a start, their diets are generally rich in legumes – lentils, beans and pulses – fresh fruit, vegetables and whole grains. They keep portion sizes small, and don’t eat to the point that they feel full.

Dr Andrew Steele, co-founder of The Longevity Initiative and author of Ageless, a guide to the science behind ageing, says: ‘Studies really do consistently show that people whose protein sources are based on beans and pulses and legumes and nuts get extra years of life and additional years of health.’

This diet may have such an impact because it’s high in fibre – a crucial nutrient that boosts gut health. Less than 10 per cent of Britons get enough daily fibre.

‘It’s hard to tease apart what it is exactly about these foods that’s beneficial,’ says Dr Steele. ‘But they also provide fibre – which you wouldn’t get from a steak.’

Our young-at-heart readers all cook from scratch – although they don’t necessarily consume lots of legumes.

Mrs Turner says she ‘can easily reach 4,000 to 5,000 steps a day just indoors’

Chrissie Turner, 80, from Eastrea, Cambridgeshire, who has now outlived all of her family – including, tragically, a son who died aged 53 of a heart attack – said: ‘I don’t buy any ready-made food at all. I have a fully vegetarian meal once a week, and fish a couple of nights. We’re not big meat eaters and I don’t eat big portions. Never any junk food.’

The experts say this is a healthy approach as ultra-processed foods, or UPFs – typically defined as containing industrial ingredients you wouldn’t find in a home kitchen – have been linked to a higher risk of chronic diseases and earlier death.

One large study based on the UK Biobank – which contains the ongoing health data of 500,000 volunteers – found last year that people eating the most UPF foods were susceptible to faster biological ageing.

Being active – both socially and physically – is also crucial.

Professor Bellantuono says: ‘What [people in the Blue Zones] have in common is a very active life, a sense of purpose, and they’re rooted in the community with lots of social contact.

‘They are active not because they necessarily go to the gym, but they might have a vegetable patch, or they go out every day with friends for a walk.’

In each case, our readers were active – albeit not gym devotees. This also reflects what has been noted in Blue Zones, where regular activity is built into daily life and where people tend also to be highly social.

Mr Squance, a retired chiropodist from Wells, Somerset, plays golf and goes walking and cycling. Since retiring, he and his wife Karen have worked as exam invigilators which they ‘absolutely love’. But he has also been involved in amateur dramatics for more than 50 years, which gives him a social life with a broad community of like-minded people, many of them much younger.

‘I love the social side and being on stage,’ he said, ‘but it also forces you to memorise lines, which keeps your brain active. I’m sure that’s helped me.’

Gillie Coghlan, who lives in the Cotswolds with husband John, the founder drummer in Status Quo, is also highly active and is busy promoting Spud, a biography of John that follows his music career. ‘So long as I can stay healthy I have no intention of stopping,’ she said. ‘People ask John when he is planning to retire, but that word is not allowed in this house. Why would you stop doing something you love?’

Chrissie Turner, who recently stopped working as an art tutor, is always pottering around her house and ‘can easily reach 4,000 to 5,000 steps a day just indoors’, while also going out with friends and heading out for walks with her husband, Geoff.

The evidence shows that it’s ‘never too late to start’ exercising, says Dr Steele.

Mrs Coghlan said that nothing scares her more than ‘a routine or settling down’

Mrs Coghlan is busy promoting Spud, a biography of her husband John that follows his music career as the founder drummer in Status Quo

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‘One study involved older adults in their 80s or 90s starting eight weeks of strength training,’ he says. ‘By the end of it they were walking faster and were generally more mobile and healthier than they had been before.’

While the optimum amount of exercise to boost health and prolong life isn’t clear, Dr Steele points out the evidence does clearly show that ‘being sedentary is bad’. ‘Lots of evidence shows even if you stand up once an hour and take a short walk, or do a couple of squats every 15 minutes, that can help,’ he says.

Our readers all described having an optimistic outlook on life, which in research has long been associated with longevity. One major 2019 study from the US found that those who were the most optimistic had significantly greater chances of living beyond 85. The most optimistic women lived on average 15 per cent longer than the least positive.

Having the mindset of a younger person also helps, says Mrs Turner. ‘Most of my friends are all 20-odd years younger than me, and I think that has a big effect,’ she said. ‘People can get to a certain age and put themselves in a box, feeling like they have to behave like an old person. I don’t.’

It isn’t optimism by itself that extends life, experts say, but optimistic people tend to exercise regularly, eat healthier diets and socialise more, while responding better to stress and recovering faster. This protects the heart, and also makes it more likely that people survive even if diagnosed with a disease.

Optimists are also more likely to sleep well – all of our participants reported no issues at all there. Regular sleep patterns are strongly associated with significantly lower risks of cardiovascular disease, diabetes and inflammation, and a longer life.

No one, however, is expected to be perfect – some admitted to a ‘bottle of Merlot’ a week, or the occasional takeaway – but as long as there’s balance, there’s a healthy trade-off to be made.

Professor Bellantuono says: ‘If you give mice a McDonald’s-style diet, they accumulate lots of what we call senescent cells – they don’t die off, and they secrete a lot of inflammatory factors that hamper the function of multiple tissues in the body. But if they follow the same diet and also exercise, they don’t accumulate these cells in the same way.’

Genetics undoubtedly also plays a role. How much remains up for debate – a study published last week appeared to suggest for the first time that our genes could play a much bigger role than previously thought, up to 50 per cent.

But some of it might be cultural, according to Professor Bellantuono. ‘The genetics factor is compelling,’ she says. ‘But we know that families also share culture – and people are likely to follow similar lifestyles as their parents.

‘If your parents cooked from scratch and were active or exercised, you will likely do the same.’

Or you can defy their example, like Gillie – whose father, a stage manager for bands, died aged 54.

‘My theory for staying young is based on the three S’s: sunshine, shopping and sex,’ she said. ‘Keep having lots of fun.’