Longevity is one of humanity"s great accomplishments.Yet it is seen as one of society"s great headaches.As the world greys,growth,tax revenues and workforces will decline while spending on pensions and health care will increase.However,those extra years of life are predominantly healthy ones.Too many governments and firms fail to recognise this fact,instead lumping all the extra years in the damning category of 65 and over.This binary way of thinking,seeing retirement as a cliff edge over which workers and consumers suddenly tumble,bears little relation to the real world.A more radical approach would start by acknowledging that,in the rich world at least,many of the old are still young.They want to work,but more flexibly.They want to spend money,too.In western Europe the over-60s will account for 59%of consumption growth in cities between now and 2030,says McKinsey,a consultancy.