Born 1953. Still here 2083

This is the John Walsh you know now: columnist, raconteur, bon viveur - well past 40 but just the right side of a mid-life crisis; This is the John Walsh you may live to see: 130 years old and wondering why the hell he's hanging on for dear life

Dateline: 24 October, 2083. Happy birthday to me! A hundred and thirty years young, and I feel fit and spry. My face is a picture. In the mirror I gaze at the dewlaps that hang from my chin like saddlebags - a spot of cosmetic surgery back in '57 didn't take, and I hadn't the heart to go through it all again - and the astounding, Galapagos-tortoise wrinkles that grid my cheeks like the cross-hatching on a Durer. Some people might find it off-putting. To me it just shouts: Wisdom.

The eyes, though, are as alert and blue as ever. Or at least, as ever since 2071, when I got the new ones. Such an improvement on the pale green ones (2064), the sexy ochre ones (2059) and the disastrously experimental pillar-box-red ones in 2055! My hair is made of the finest-quality, bio- engineered hemp follicles money can buy, back-combed, blow-waved, highlighted with cyclamen streaks in the most approved style of Senior Citizen Chic, and personally suture-welded into my scalp by Lord Nicky-Clarke of Mayfair.

I toss my head. The turkey-wattles shake. I'm a fine figure of a man.

"If Ah'd known Ah wuz going to live this long," declared the jazz pianist Eubie Blake on reaching his centenary, "Ah'd have taken better care of myself." But if we did know - if we could be certain - that we were going to live to nearly twice our biblical lifespan, what would we do about it? How would we parcel out our lives to ensure we derived the most benefit from this double-edged gift of years?

A physicist called Michio Kaku, of New York's City University, prompted these speculations with his recent pronouncement that our children, born in the Eighties and Nineties, could look forward to living for up to 130 years. It's not, thank goodness, simply a matter of living longer and spending a grim half-century bent double with senility and arthritis. Kaku's researches have been in the fields of preventive medicine, bio- engineering and genetic tinkering, and are as much concerned with rejuvenation as with staving off death. A whole range of treatments for supposedly incurable conditions, Kaku reported, is now in train. The Human Genome Project, for charting all 80,000 genes in the human body and identifying our genetic disposition towards cancer or heart disease, will be completed within the next four years. The cloning of human organs, and the growing of new body parts from human tissue are already beyond the experimental stage at Harvard Medical School.

It is possible to imagine a life in which, technically, you could replace damaged organs with new ones as blithely as getting a re-tread for your car tyres. A life in which future diseases or functional breakdowns could be anticipated and dealt with before they happened. And one in which we might suffer aches and pains at 100-plus, but needn't fear that cancer or cardiac arrest would carry us off before we had completed our 130-year stay on earth.

I've had a good innings. Retired at 65 to take it easy, read the complete works of Dickens, Proust, Tolstoy and Henry James and to do some light pruning in the garden. Nothing too stressful. Maybe the odd Saga holiday to the Lake District, nothing stronger than poached fish for supper, washed down with a nice Wincarnis. After 10 years of behaving sensibly, I thought, "Stuff this for a lark", got myself a reconstituted bladder, lungs and ticker and took up snowboarding in the Dolomites, then graduated to wing- walking on Stealth bombers. It tests your nerve, of course, but (now that I've grown a new liver and kidneys) I find a shot of absinthe before take- off steadies your resolve. I enjoy holidays, and a digestion, that I previously never dreamt of. The wife comes along too, but she finds it hard to cope with my gross and relentless sexual demands since I had the new hampton microsurgically fitted on my 82nd birthday.

We can, in theory, think the impossible about our lives. Could we extend childhood by deferring puberty until our early twenties? Will education in the next century extend from its present average of 12-16 years to 20 or 30 years? Will retirement mean a succession of holidays, or a cultivation of the spirit in a late burst of education? What will it be like having a mid-life crisis at 80? Will people refrain from having children until their fifties? As golden wedding anniversaries become commonplace, what shall we make of the 100-year wedding anniversary? Will couples routinely split up after their children leave home, and re-embrace the single life until driven to look for a new partner to see them through the next few decades? Will an average career feature three or four marriages and a dozen children?

When the wife died I was sorry, of course, but I was still a young man - 89 - with a leftover life to live. So I married a sixtyish microbiologist called Maureen. Thanks to the leaps and bounds of endocrinal research in 2042, we had three children. All grown up now, of course. Sam, our eldest, has just finished his seventh degree at Ruislip University. His exam-results party coincided with his 40th birthday, so we had a high old time. I bought him a Genetic Sequencer, latest model, a bit like one of those dashboard whatsits back in the Nineties, like an illuminated A-to-Z map, which warned you about imminent traffic hell. This device warns you that your cholesterol is silting up like crap in an S-bend, your liver is bulging like ripe Brie, and your spleen's about to explode. It's a fun sport, diagnosing things that may happen, now that they've eliminated cancer and there are no life-threatening diseases except boredom...

There used to be just two ages: childhood and work. In earlier centuries, death brought the working life to a sudden stop without any benign hinterland of retirement. It was Otto von Bismarck, the German chancellor, who invented the state pension in the 1880s. Suddenly there were three ages: childhood, working life, retirement. Ten years ago, owing to revised attitudes to work and leisure, four ages were identified: education until you're 21; work until you're 55; then a "Third Age", devoted to travel, learning and self-improvement, until you're 75; then a final, sans-hair-sans-teeth period of 15 years or so until the Reaper comes to get you. Now, how shall we divide it up? Perhaps into five ages: education up to 30, work to 60, then a five-year gap, like a creative siesta, while you cultivate your interest in watercolours, then a return to work until you're 100, followed by a 30-year wind-down of sedentary pursuits.

This is not a fantasy. We've already made ourselves live longer than evolution dictates. In 1900 the average life expectancy of British humans was only 50. Today the average life expectancy is 77. This tinkering with longevity flies in the face of nature, which designed us to become obsolete once we'd completed our task of bringing up the next generation. But we shall go on extending the human time-scale; more and more people are now sailing past their 100th birthday, intact. For the first time in human history, centenarians are one of the fastest-growing sectors of the world's population.

There's a lot to be said for going on and on and on. When they woke up Woody Allen in Sleeper and told him he was more than 200 years old, he asked: "Does that mean I'm coming to the end of my Freudian analysis?" Living for ages means you can lay down a fantastic cellar of Chateau Petrus, confident that you can give it a half-century of maturation. Having more time won't mean you'll become suddenly talented at things you couldn't do before, but you could improve your fairway technique immeasurably. And you can read the whole of A Suitable Boy without feeling you've devoted too much of your life to it. The House of Commons is full of centenarians who, ages ago, voted to increase the life of a government from five years to 10. "What's all the rush?" became the standard line on emergency legislation. You'll never get near the Cabinet office until you're 80. It makes for a restful debating style. The House of Lords, meanwhile, is like a museum. Some of the exhibits claim to remember Sir Alec Douglas-Home.

The present Government's own statistics suggest that, by the year 2050, the average lifespan of men and women will have increased only to 79 and 84 respectively; they're not as au courant as Professor Kaku, but they know there are problems on the horizon. At the DSS, the pension figures are alarming. The number of retirement pensions being paid in 1980 was 9 million, and the total expenditure on them was pounds 14.7bn. In 1997, 10 million pensions were paid out - and expenditure had more than doubled, to pounds 33.6bn.

Last December, Alistair Darling announced the Social Security department's prognosis. He foresaw 15 million pensioners by 2050 and a gradual drop in state support. To avoid having the nation filled with poor and mutinous old people, like the multitude of vieillards begging for death at the end of John Boorman's Zardoz, he suggests that the better-off should look after themselves ("Everyone who can save for their retirement has a responsibility to do so") while poorer people would be granted a state second pension of pounds 50 a week. If the scientific spec- ulations from California and Harvard carry an ounce of truth, however, such provisions will be pitifully inadequate.

OK, there are a few downsides to all this. Seventy-five-year mortgages are a bind - you never seem to get near paying them off - but they're a necessary evil, now that house prices are all in the millions. (There's no such thing as a "quick sale" any longer; even the survey and search take at least a year.) The children from my first marriage complain that they won't inherit any of my cash until they're too old to need it; but I'm not going to hand over my money just yet, thanks - the 100-year savings scheme is maturing nicely. It made for a certain tension in the family. I had to ask them to leave (but then they have been living here for 60 years). Sometimes I'm shocked to think that the leisure industry is the most important on the planet. And I'm frankly bored rigid discussing symptoms and viruses and self-diagnosing machines, which are the only topics of conversation now. But however dull it gets, hell, it's better than the alternative.

But we could have got it all wrong. None of the above may happen if, as some predict, the human body will keep on dying from simple exhaustion. "Curing heart disease and cancer tomorrow would increase lifespan by about 15 years," said an American professor of anatomy, Leonard Hayflick of the University of California, "but the fundamental, inexorable ageing process would continue." We don't know. We'll only find out later. You know what they say: life begins at 110...