Dateline March 15, 2037, Anne Johnstone, aged 86, somewhere in Scotland: "Sunny day, so jogged for half an hour before breakfast. (These new knees are wonderful.) Filmphoned my daughter in Australia and chatted while she prepared dinner. She looked worn out. Told her she was working too hard. (She said I looked great, adding cheerily: "We'll need to shoot you.") Tried some Sudoku to give the grey cells a workout, before heading off to the primary school with my girdle (sic!), to inaugurate P6 into the magic art of potato scone-making. Lots of fun and flour. Then visited my great-grandson, using my free travel pass. Stayed home tonight to write a book review for The Herald, to supplement my paltry pension. Frosty night but I'm cosy in my triple-glazed, solar-powered, carbon-neutral bungalow."

According to the Scottish Executive's new strategy for our rapidly ageing population, this is the sunlit future we babyboomers can contemplate as we start heading for what is known with increasing irony as "retirement".

Even if the numbers have crept back up recently, the 55,690 births in Scotland last year represent barely half the 90,639 bonny bairns who first saw the light in my birth year, 1951. Certificates in mathematics are not required to work out that if my generation adopts the "pipe and slippers" approach to life after 65, we are all doomed (even without the pipe).

If there is a key statistic it is that by 2031 the number of over-75s is going to rise by 75%. With such a dramatic shift in the balance between what has traditionally been regarded as the working population (18 to 65-year olds) and the rest (mainly children and senior citizens), the whole notion of retirement must be reinvented.

The death rate is as important as the birth rate in creating this seismic shift. We are becoming increasingly death-proof. In the past 10 years fatal strokes and heart attacks have fallen sharply, thanks to better health, earlier diagnosis and better treatment and aftercare.

This has had an adverse impact on cancer deaths as those who would have keeled over from cardiac and circulatory problems, succumb to the Big C, but scientific advances are now making many cancers eminently survivable, too. There's always Alzheimer's and Parkinson's but stem cell research could one day produce treatments for these terrible twins too, opening up a rather startling vision. Soon could we be going on and on?

In 150 years life expectancy has doubled from 40 to 80. As science comes up with ever more inventive ways of renewing and repairing our bodies, the notion of three score and ten as a respectable lifespan becomes outdated. Cambridge gerontologist Aubrey de Grey believes the first person who will live to be 1000 is already alive and 150 is eminently achievable.

As it happens, pupils will gather in Edinburgh tomorrow for the Scottish finals of the Institute of Ideas' Debating Matters competition. The motion? "Attempts to extend radically the human lifespan should be welcomed, not feared." Naturally, as a judge I'll be assessing how well they argue their case and stand up to cross-questioning, but I know which side I'd prefer to be on.

It may be easier to support the motion. Expanding lifespans are a fact, after all. In 1899 there were probably about 10 centenarians in Scotland and we know nothing of their frailty or mental capacity. When I set out to track down Scotland's "super-old" in 1999, there were more than 1000. Journalism has rarely bestowed on me a greater privilege than chatting with these women and men born in the reign of Queen Victoria: Lizzie Crawford, discussing the pros and cons of mini-skirts; Alfred Anderson, visiting his 80-year-old daughter in an Eventide home; Chrissie McLaren, who had reluctantly given up chopping her own wood at 102. It was as if they had outlived age.

The point was that we are not just getting older but staying fitter for longer too. Today about 35% of our over-75s do some volunteering work. Seen in this light, what we emotively call "the demographic timebomb" looks like a blessing in disguise.

But hang on. Just because some people's longevity defies our expectations, just because we CAN stretch lifespans, doesn't mean we should. There is a counterpoint to the upbeat fantasy with which I began. It is the fear that the reality will be not an active, engaged octogenarian but a whiskery chin, incontinence pads, forgetting my children's names and countless tedious mini-bus outings to Aberfoyle.

Let's face it, two barriers need to be pushed forward together here. Longer lives can be seen positively only if the age of decrepitude continues to rise in parallel. Otherwise we create a caring crisis for both society and individuals.

Last week Scotland's Care Commission announced an inquiry into the use of sedatives and anti-psychotic drugs in care homes, raising a nightmare spectre associated with the term "granny farming". As the battalions of babyboomers start losing their marbles, how will we cope? Many hard-working middle-aged friends are already worn out by looking after both children and elderly relatives. What if there were several generations of progressively wrinklier rellies to care for? I enjoy getting to know my great-great-grandparents through a spot of genealogy without the slightest desire to visit them every Sunday.

The biggest misgiving about extreme anti-ageing research must be that it will succeed in preserving our bodies without effectively tackling our minds. I am still haunted by the vision of my late mother-in-law with her perfect skin and hair, beautiful intelligent eyes and text book heart, but no longer capable of forming a sentence.

We should be uneasy, too, about comparatively few, mostly well off, people in the west inhabiting some exclusive sunny upland beyond old age while men in Shettleston have an average life expectancy of 64 and the typical Zimbabwean is lucky to see 37.

So, while it would be absurd to ban anti-ageing research, if our society has any pretensions to tackling social justice and shrinking grotesque inequalities, we should concentrate resources on improving the health and lives of the poorest, not the oldest. We should be grateful that Bill Gates and Warren Buffet are not investing their billions in trying to acquire for themselves the immortality of Greek gods but are more concerned about Aids and malaria that are robbing millions of African children of their parents and teachers.

Last, and most crucially, we should resist the notion that we can all be Methuselahs because this treats death as a problem, an obstacle, a defeat. In The Herald Magazine last Saturday, Sally Magnusson treated us to the most eloquent tribute imaginable to her late father Magnus. As he approached his end, the gruffness and grumpiness in his character seemed to give way to his gracious and affable side.

My family witnessed this for ourselves, stopping to greet the author and quizmaster at a table outside the Milngavie cafe he adopted towards the end, still pulling on his trademark pipe. And though we cried when he died, there is no doubt that his dignity in death was a triumph. Without such paradoxically life-affirming experiences, we might find we have less to live for.