For some people, old age is like a mirage: always on the horizon but never reached – by themselves at any rate. When my father was in his early eighties, he referred somewhat disdainfully to his neighbour, eight years younger than he, as ‘the old man’, but he never applied the epithet to himself. And while children often long to be older than they are, no one longs to be old.

For the first time in history, however, most humans born will reach old age, whether they like it or not. Also for the first time in history, the old will outnumber the young in many countries. No subject, then, is of wider or more immediate personal concern than