The generations of Windsors who emerged stiffly in wintry clothes at the end of their austerity cruise in the Western Isles last week were regarded as quaint, but the Royal Family is evidently a model for the future. There is a doughty matriarch of 84, working full time and supporting many dependants; a son kept out of a job because there is no longer a retirement age to create a vacancy; anxiety about members of the extended family who are on benefits, since taxpayers' tolerance of subsidy is perilously low; a young prince who keeps trying to push back his wedding day because the ratio of 27 years being single to 72 years or so of married life is hard to swallow.

Most of the discussion around an increase in life expectancy has been about work and pensions. There's not enough in either our own or national pension pots to pay for extended retirement, so we're going to have to work longer. Boris Johnson suggested last week that 80 was a more realistic retirement age. But there is a deeper question than how we shall make ends meet, which is whether we begin to live our lives differently once we expect to have an extra 20 years. Surely we must learn another rhythm, a longer perspective. There is suddenly a multitude of possibilities and fewer reasons for regret. Lost time can be regained.

For generations, women churned out six children by their twenties. Now, responding to a different time frame and in an age where many women regard their bodies as their own, they wait until their thirties. The tensions of working motherhood, rehearsed so attentively by the Daily Mail, will evaporate once women start entering the job market post children. Perhaps we shall achieve a work/life balance by spending 16 years raising children and then 50 years at work. When Yvette Cooper declined to run against her husband Ed Balls for the Labour leadership, she said that there would be plenty of time for her career once her children were older. Cooper was minister in charge of work and pensions, so she should know.

If we're going to live to Old Testament ages, we can have children, work and cougar as much as we like. Even Naomi Campbell would feel she had had enough me-time. We can eke out the landmarks of our life, or else repeat them or, most wondrously, believe that life has a third act. The great accomplishment we will all have to learn is patience.

I married relatively young. My elder son has done the same. There is thus an unlikely but theoretical possibility that I could be a grandmother before I am 50. Just now it feels rather like being a washing machine that has gone through all its cycles and finds its programme finished. What I should be looking to, of course, are unexplored horizons. In the new world, forties is late adolescence, 60 is middle age. Even in our nineties, we need not be skeletal and enfeebled: we can be P D James.

We can learn that the pleasures of the young do not fade, so much as become affordable, particularly if we go on working. I once attended a brain-storming session to create businesses for new consumers. The idea that scored highest in research was beauty treatments for women over 70. They were being offered stairlifts and hearing aids. They wanted spas. Older people are eager for the Open University, computer skills, cookery tourism, gap-year volunteering. The third act may be a reprise of the first, but who says we can't write in a crescendo?

Sarah Sands is deputy editor of the 'London Evening Standard'