And when an Edinburgh psychologist called David Weeks placed an ad in New Scientist for Superyoung types to contact him, he got more than 3,500 replies from people aged from their twenties to 101. They all sent photographs; and, he says, they really did look 10 to 12 years younger than they actually were.
Dr Weeks believes the Superyoung not merely look good; they are also having a good time. They are fit, zestful, interested in everything; they even, according to Dr Weeks, have loads of great sex. He thinks 'ageing definitely appears to be related to mood. I believe the elixir of life is between your ears'.
The poet Hugo Williams thinks it's got more to do with your nose. Williams is 51, and feels 'very insulted when people say I look in my early forties', so used is he to being thought in his late thirties. An insubstantial nose, he says, is a vital asset here. (This is a point echoed by Tony Elliott, owner of Time Out magazine, who is 46 but thinks, 'I could get away with claiming 34, just about,' an advantage which he ascribes partly to having 'a small nose, which is turned- up'). Williams also recommends full lips. 'Mine were very full when I was young, which means when they de-balloon they don't look awful, whereas most people's collapse.'
Richard Edwards, a British solicitor now living in New York, was refused permission to buy alcohol in a Florida store when he was 34: in Florida, liquor is not sold to anyone under 21. Edwards thinks looking young 'is about 80 per cent genetic, 20 per cent state of mind. My parents looked young, and my eldest sister, who is 40, regularly gets taken for someone in her twenties.' Like Williams and Elliott, he suspects size matters: 'Americans rarely look younger than they are, because they are all so big.' And he supports David Weeks's theory that attitude is crucial: 'I'm very optimistic. It sounds Pollyanna-ish, but it's true. I'm just positive.'
The Superyoung tend to think that you can't choose your parents too carefully. (Hugo Williams claims - rather extravagantly - that his mother had world-famous cheekbones). 'Good skin makes a huge difference,' says Eleanor Blake (63, looks early fifties), 'And avoiding weight helps: most women my age find their hips just spread, and I really don't think there's anything you can do about that.' David Weeks, however, persists in believing that 'heredity is not that great a factor: it's more about how you have kept yourself stimulated psychologically and physically since early adulthood'.
For Hugo Williams, looking young is not about rushing round frenetically. 'I've probably aged less fast because my mental turnover is so slow.' Most of the Superyoung, however, do not regard energy as a finite resource, but as something to be avidly consumed. 'It is important not to waddle,' notes Eleanor Blake. 'Some people walk properly - quickish,' says Tony Elliott. 'It's a metabolic thing in a way: I have quite a high adrenalin level. People who look older tend to be a bit slow, don't look as sharp. They seem depressed.'
Jean Hatton, a medical secretary and part-time model, who admits to being in her late-fifties, says (in the rather smug way that the Superyoung have) that it is important to feel you are learning things all the time, that life holds potential: 'I went sailing for the first time recently, in gale force winds.' Barbara Follett, the founder of Emily's List UK, who is 50 but could get away with pretending she's 10 years younger, says: 'There is a magic moment in a woman's life when she is the right age. I think it's about 43. The important thing is not to give in when it passes.' Posture is vital here, she thinks. Eleanor Blake agrees - 'and being able to duck under barbed wire when you are out for a walk. And not buying coats just because they keep you warm.' The Superyoung, while disapproving of 'mutton dressed as lamb,' are extremely style-conscious.
There are, Dr Weeks explains, many theories about the factors that may speed up or retard ageing. 'Cardio-vascular disease is known to slow the mind, so that people seem about eight years older than they actually are. Living in poverty has the same effect. Looking young is much easier if you are affluent, and have always had a fairly stable life. The sun, smoking and a lot of facial expression are all bad.' There are also more outre theories: that sugar interferes with protein synthesis - 'a minority view,' says Dr Weeks, tipping saccharin into his tea. Or that one gene accelerates ageing and another decelerates; or that certain vitamins and minerals act as 'free radical scavengers,' gobbling up pollutants which, as it were, rust the body's working parts. Or that the whole process is a war of attrition against the immune response system, repaired by occasional spurts of human growth hormone, produced by stress.
As a psychologist, however, David Weeks was interested to observe that many of the depressed people he was seeing looked older than they really were. It was as if their mental state was taking a toll on their looks. The Superyoung - whom he researched through postal questionnaires - are, by contrast, not depressed at all. (One is inclined of course, to snap: 'Well, no, they wouldn't be, would they?')
The commonest Superyoung shared feature was activity. 'They aren't keep fit fanatics, but for most of their lives they have walked an extra two or three miles a week, and they are the sort who walk upstairs rather than use lifts.'
The second most important factor, according to Dr Weeks, is an 'exceptionally good sex life. The Superyoung are always in relationships, romantic relationships, in which they can communicate with their partner. They would hope to stay - they are not unconventional people, don't hold radical views - but if they weren't satisfied, they would leave. They frequently have younger spouses.' (Dr Weeks goes on about sex at quite some length, pointing out that it releases something desirable called beta-endorphins.)
The final common Superyoung factor is optimism: 'They are very interested in things generally, involved and pro- active. They prefer to have an argument and get feedback than let their anxieties fester. There are very few couch potatoes among them.'
We are always being promised that older people are about to come into their own. The sad truth, however, is that societies in which old people are revered are invariably slow-moving; in the developed world, technology is now so fast-moving that the young always seem to know more than their elders: it is unlikely that anyone will go back to painting grey into their temples in the foreseeable future. The pace of change, more than the fact that old means nearly dead, is why there is such an imperative to keep young and beautiful. Young, paradoxically, equals wise.
The Superyoung seem to have it all ways: they have the wisdom of age, but they also appear to have the wisdom of youth. When not bounding upstairs or romping around having an ecstatic sex life with some younger partner, they are ducking under fences, working as part- time models, or simply looking in the mirror admiring their small, perfectly formed noses. Oh, but come on, there must be some drawbacks? It's a bit of a bore, they say, when you are 20, and people think you're 14: the great sex life can be a bit slow getting going. And there's always that terrible fear, when you let slip that your younger child has just gone to comprehensive, that someone, someday, won't say, 'You have children? My God, you only look about 21]' That can be quite a worry.