The "mid-youth" society - its replacement - has distinguished members. Goldie Hawn, Helen Mirren and Joanna Lumley have all celebrated their 50th birthdays in the last year, and their appeal is greater than ever.
Ms Lumley may have first achieved fame in the 1970s with the New Avengers but will be remembered for her 1990s' triumph - the chain-smoking, coke- sniffing, drunkard Patsy in Absolutely Fabulous. Ms Mirren has been working for the Royal Shakespeare Company since her 20s but had her greatest success as Detective Inspector Jane Tennison in Prime Suspect. Last week, Ms Hawn, with a career of 30 years behind her, was photographed in London looking amazing in a see-through T-shirt and figure-hugging trousers. Her partner, Kurt Russell, has described her as "a phenomenon. She looks 35 and a healthy looking 35 as well."
They are not the only ones. Susan Sarandon, 49, won her Best Actress Oscar this year for Dead Man Walking and Jane Fonda, 58, has gone through the careers of actress, aerobics guru and revolutionary and is now married to billionaire Ted Turner.
But while we have grown up with the image that Hollywood stars never fade, they just get another facelift, the signs are equally strong in real life.
Opening photo albums at a recent family party was a shock: I looked at pictures from 1971 of my aunt's wedding. My relations looked middle- aged. Glancing at my mother, Carys, across the table I realised she was a good 10 years older than the figures in the photos, yet at 52 she looked 20 years younger than them.
Nearly 30 years separate my mother and me, but look at us together and it seems half that. And she is not the only one. The concept of the 40- year-old woman worn out by years of childbirth, settling down for a quiet life of slippers and Scrabble is outdated. She is far more likely to be the Peugeot 306 woman in a little black dress, whisking her husband off for sex on the beach before returning home to her two children.
The cult of youth is such that according to the Wrinkle Report, a Harris poll of 1,200 men and women aged 30 to 50 in the United States, three out of four baby boomers - the immediate post-war generation - think they look younger than their years. Eight out of 10 say they have fewer signs of facial ageing than their peers, (a situation that is statistically impossible according to a spokesman for the pollsters).
Maddy Kent-Dytchwald, described in the report as a "nationally recognised expert on the boomer generation", says a typical 45-year-old feels 15 years younger: "Boomers are redefining what is young so they can be included in the definition. In fact, the stage of life they're entering might not be called middle-aged at all but 'mid-youth' instead."
There does seem to be some truth behind the picture of mid-youth Dorian Grays. The boundaries of middle-age have changed as our life expectancy alters.
Had you been born in 1841, you could expect to live to 40 if you were a man, and 42 if you were a woman, which places middle age somewhere round 21. By 1950, this had risen to 66 years and 71.5 years respectively. Male babies born in 1993 can look forward to 73.8 years of life and females 79.1.
Dr Sidney Jones, a psychologist with an interest in lifespan, says that basic but radical changes in the way we live have contributed to the redefinition of age. "Between 1900 and 1930, the average height of 13-year-old boys went up two-and-a-half inches. That is an enormous amount in 30 years. Health has a big effect on how people feel. If you are healthy you feel better," he said. People are better nourished than they were 50 years ago, and many threatening diseases - tuberculosis, scarlet fever and diphtheria - are rare in the UK.
One of the biggest tolls on women's health, frequent childbearing, has almost ceased thanks to the Pill and the decisions to marry and have children later. On average, women marry at the age of 29.9, four years later than in 1940. The fertility rate has dropped from 2.93 in 1964, to 1.8 and about one in five women will remain childless.
Many delay having children until they are in their 30s. "A lot of the risks previously thought to be associated with having babies at a more mature age were based on women who had had a lot of children, and who were not well-nourished or healthy," said Professor David James, professor of feto-maternal medicine at Queen's Medical Centre, Nottingham. "Women who choose to have babies later are often healthier, from a higher socio- economic background and have chosen to limit the number of children they have. The only risk we have to warn them about is that of Down's syndrome."
But the difference between the middle-aged now and those half a century ago is more social than physical, argues Dr Jones. These include a more prosperous society, better housing, shorter working hours and improved education. "People aren't starting work until they are in their 20s. It also changes ways of thinking, the levels and range of interests."
It was once said that the three most important advances for women's lives in the 20th century were the vote, the Pill and the washing machine. The emancipation of women in the last 100 years has been a major driving force in pushing back the boundaries of age.
"Women are no longer dependendent on men economically. Marriage is no longer necessary," said Dr Jones. "In many cases, women are becoming the driving force in social change."
Dr Kevin Morgan, senior lecturer in gerontology at the University of Sheffield, argues cultural changes have been just as important. The difference is in what we do, not what we are.
"Age-specific activities used to tell us how old we were. It was the question of 'acting your age'. If you looked back to 1956, you wouldn't find 40-year-olds engaging in strenuous physical activity, there wasn't the same concern about keeping fit and going to the gym. And there was no question of 50-year-olds listening to the same music as 16-year-olds.
"Now the distinctions have blurred between older and younger people. The absolute judgements have gone.
"It's part of the general postmodern trend. What happened was the value of retaining rigid roles simply eroded away."
For Dr Morgan significant events that chart the shifting revolution took place after the Second World War - Jack Kerouac and the Beat generation, Bill Haley and the growth of rock'n'roll. "This generation defined itself as culturally different. But if you establish a youth cult what happens when time keeps moving on and you're no longer the person you were? You have to keep being young, there's actually a kind of inverse logic to it. A classic case is Mick Jagger who is in his mid-50s. There seems to be no on-off mechanism for him."
Our obsession with youth has led a clinical neuropsychologist to conduct a study into the "superyoung" - 3,000 people between the ages of 19 and 102 who look 12 to 14 years younger than their actual age. Dr David Weeks, of the Royal Edinburgh Hospital, has been looking at the ageing process and the connection between ageing and ill-health.
So what are the secrets of eternal youth? The superyoung usually take regular exercise (and tend to have done so since their late teens or early 20s), have happy marriages or partnerships, often with someone younger than they are, and mix with younger people.
Few smoke and, in the case of post-menopausal women, many take hormone replacement therapy. Their diets are not unusual but there were 5 to 10 per cent more vegetarians than predicted. Dr Weeks estimates that the superyoung number "about 1 per cent of the population".
As I pray that my mother has remembered to leave her genes to me, the question of the future remains. Can we all continue to get younger and younger, abandoning knitting for nightclubs, or will Dorian Gray's picture eventually be smashed?
Don't worry, is the answer. The fab 50s have a long way to go yet, as demonstrated by Noel Coward's Elsie, who elucidates the most important points of acting your age in the1938 production Set To Music:
"We talked about growing old gracefully
And Elsie, who's seventy-four
Said 'A: it's a question of being sincere,
And B: if you're supple you've nothing to fear'.
Then she swung upside down from a glass chandelier,
I couldn't have liked it more."
How to mask the march of time
Ten top tips:
1. Choose your parents wisely. Genes and bone structure always win out.
2. Get someone else to have your children. Cuts out the worry of stretch marks.
3. Hormone therapy - HRT or testosterone patches.Teresa Gorman swears by it.
4. Desert your own generation and go out with a toyboy. You're as young as the man you feel.
5. Join a gym. Regular exercise can't be beaten (also good for meeting toyboys).
6. Dress to kill. Even M&S have brought themselves up to date.
7. Watch Top of the Pops again. Most of the bands on it will be your age anyway.
8. Forget gardening, Monopoly and quiet nights in. Relive Saturday Night Fever instead.
9. If in doubt, cheat. Face lifts, tummy tucks ... Everyone else does it.
10. Remember the words of Bernard Baruch: Old age is always 15 years older than you are.Reuse content