Here's a puzzle of our times.
A woman and a man sit side by side on a bus. She is 65 and appears younger. He is 38 and looks older.
She exercises regularly, eats a healthy diet and enjoys socialising with family and friends. He smokes, drinks too much and lives a sedentary and solitary existence in front of a computer and the television.
She might live to 100. He might live to 65. She might have 35 more years to live, while he has 27. In which case, which of them is the older?
In this era of long life for those who live sensibly and moderately, should we measure age from the cradle or to the grave?
We do both. It's how we find the middle – and it's why the middle has us in a muddle. Life expectancy is lengthening so age brackets have become elastic. Accordingly so has behaviour.
The news that Judy Steel got a tattoo for her 70th birthday catapulted her onto Radio 4's Today programme yesterday. She sounded slightly bemused since her leaping leopard is two years old. It's on her shoulder, mostly out of public view.
Is it inappropriate in someone of her age? I don't think so. However it begs the question: are age barriers history?
They used to be so rigid. When I was 29 years old a friend asked when I was going to have my hair cut short. "We'll be mutton dressed as lamb if we have long hair at 30," she told me solemnly.
Today's 30-year-olds are often still single and dating, never mind over the hill. Age, we are discovering, is a fluid commodity.
Pensioners can and do look like Sandra Howard and Marie Helvin. It isn't just the famous who are looking better for longer. The once ubiquitous race of small, round woman with permed hair and sensible beige shoes is an endangered species.
Medicine and good nutrition deserve thanks but attitude too is crucial. Scientists believe personality is a major factor when determining lifespan.
A study of centenarians carried out by the University of Georgia in 2010 found that a person's ability to adapt to stressful situations and cope with them was a crucial factor in determining their lifespan.
What happens to you matters but even more telling is your perception of what is happening. How a person feels about their health and quality of life is a stronger predictor of survival than blood pressure and blood sugar levels.
Open, conscientious people last longer than the neurotic.
Okinawa in Japan has the highest percentage of centenarians in the world. Analysts have identified five causative factors: a diet of grains, fish and vegetables, a low-stress lifestyle, a caring community, high levels of activity and spirituality which gives a sense of purpose.
It doesn't mention tattoos but it's easy to spot the parallel. Getting a tattoo at the age of 70 is surely the symbol of an open and optimistic individual.
It speaks of self-confidence, a strong sense of individuality and a devil-may-care attitude. It's an act that is devoid of neurosis. Quietly flying in the face of convention demonstrates that you are easy in your own skin.
People born in the UK between 1955 and 1972 have a 15-20% chance of reaching their 100th birthday. One-quarter of girls born in 1982 will make it as will one-third of those born in 2011.
So when will they be middle-aged – at 50 or 60? How long will they need to work? Will they have one career or several? How long will their marriages last? They are already marrying later. Will they also marry more often? Or will marriage and child-bearing become a minority part of an essentially singular life? It is a salutary thought.
My mother was married for 50 years and yet was single for half of her life. She was born in 1910 which meant that statistically she had a 1% chance of reaching 100. She died aged 102. She told me that, had she known, when she was widowed at 72 that she still had 30 years to live, she would have spent those years very differently.
She came from a generation where women lived quietly and domestically. Today we know better.
It is life enhancing to pass leather-clad bikers on a Highland road and realise their average age is 50. It's pleasing to hear that one-quarter of the over-55s are planning a gap year or have been travelling. Is 80 old? I know someone fast approaching it. She is planning a trip to Antarctica.
A year spent travelling, like a discreet tattoo, says you aren't hidebound by the numbers on your birthday card.
I read on Sunday that the still handsome writer, Elizabeth-Jane Howard, now 89 years old, is open to the possibility of finding a last love with whom to "skirmish on a chaise longue". This, despite her poor lungs, arthritis and zimmer frame.
Like Judy Steel, she seems to be travelling in hope with her spirit undimmed.
It's not about maintaining a coy and unfortunate flirtatious sexuality. It's not about clinging to a mini skirt and diving neckline with knobbly knees and an inappropriate cleavage. Where collapsing age barriers do people a disservice is when they fail to spot that a moment has passed.
Judy's example has more to do with joie de vivre – an essential ingredient in the new reality for the concept of retirement has also evaporated. Real people are living like the characters in The Best Exotic Marigold Hotel. Many have seen the promise of a financially comfortable retirement dissolve on their approach like a mirage.
From now on, a very select few will be able to coast after 50; to become observers of life rather than participants. It's not just about having a tattoo. Increased longevity means people will need to keep themselves fit and mentally alert in order to remain part of the game; in order to survive financially.
They are challenged with gathering their resources and finding a fresh economic path forward. To succeed people need to forget their age and see themselves as they are.
It's all a matter of attitude and personal choice – so when you find yourself wondering if - the answer is, why not?
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