Where will it all end? That is an economist's question. For those of us alive today who may yet reach 100, there is another question: would we want to?
The UK's Office for National Statistics has estimated that nearly 40 per cent of girls born this year will live to be 100, rising to 60 per cent for those born in 2060.
Boys are not far behind. What we cannot know is whether, if asked, they would choose to live so long.
Jonathan Swift understood the question. Gulliver's Travels features a race of humans, the Struldbrugs, who were normal in all respects except one - they did not die. But their immortality, instead of being a blessing, was a curse, because they continued to age.
"At 90, they lose their teeth and hair; they have at that age no distinction of taste, but eat and drink whatever they can get, without relish or appetite. The diseases they were subject to still continue ... the question therefore was not whether a man would choose to be always in the prime of youth, attended with prosperity and health but how he would pass a perpetual life under all the usual disadvantages which old age brings along with it."
In a recent Independent article, Walter James, who celebrated his 100th birthday last year, wrote movingly of the deprivations of age, not on his body or mind, but on his emotions.
Though he still shops, cooks and looks after himself, does the crossword, enjoys a glass of whisky and can recall events from his past with clarity, what he cannot recover are the feelings and sensations that accompanied the events.
Recounting his sporting successes and sexual adventures, he notes the absence of the excitement and exhilaration that went with them. "My memory has kept the bones but lost the flesh around them."
He adds: "Perhaps the greatest loss is what it is like to be in love. I can remember the routines of being in love, the shared meals, concerts and theatres, walks in the country.
But writing all this is like taking a book down from the shelf and leafing through its pages. What escapes me is that extraordinary sense, which so many share, of being in love."
Such observations are bound to make those younger wonder - is ageing, at the rate those of us fortunate enough to live comfortable lives in the West are achieving, something to be celebrated or feared?
The pace of advance is astonishing. As recently as 1980, scientists believed that age 85 would mark a natural limit for average life expectancy. In Japan that barrier was passed for women in 2007.
In Britain, the average life expectancy for both sexes born today is over 90.
What is the secret - the elixir of life? It is not some fancy nostrum. Just better standards of living, education and healthcare. Dull, perhaps, but marvellously true. In the early part of the last century, improvements in infant and child survival contributed most to growing life expectancy, but since the 1950s the biggest gains have been in the over-80s - the pay-off for improvements in how we eat and drink, where we live and what we do.
What worries most people about ageing is losing their faculties and the ability to perform the daily tasks of living - eating, dressing, bathing and getting around.
The trends in this regard are worrying.
The good news is that despite increases in cancer and chronic conditions such as diabetes and arthritis, earlier diagnosis and improved treatments have rendered these conditions less disabling.
In the future, more of us will fall ill, but the illnesses should affect us less. The result is that we may live to see our great-grandchildren and even our great-great-grandchildren.
The bad news is that there are large differences between countries in healthy life expectancy beyond 65 - that is, years spent without disability.
According to the 2010 Global Burden of Disease study, over the last 20 years healthy life expectancy in the UK has increased for women by 3 per cent at birth while overall life expectancy has increased by 4.6 per cent.
If ageing is to be celebrated we need answers to the personal, social, financial and health challenges it poses. One suggestion, proposed by Professor Kaare Christensen, of the Danish Ageing Research Centre, is to extend working lives by shortening the working week. It would be a way of keeping more people busy, solvent and socially engaged.
"The 20th century was a century of redistribution of income," Professor Christensen says.
"The 21st century could be a century of redistribution of work. Redistribution would spread work more evenly across populations and over the ages of life.
Preliminary evidence suggests that shortened working weeks over extended working lives might further contribute to increases in life expectancy and health."
Work till you are 100? Now that would deserve a celebratory telegram.
- Independent
