Attitudes to ageing tend to be negative. Older people tend not to be valued highly, more often seen as a burden rather than an asset. Is this a new phenomenon, linked to the growth in the number of older people?

Why do we have an obsession with looking younger? Perhaps we don't like to be reminded of our impending mortality - each age-related decline is a sign that our end is more nigh. Perhaps a stronger motive is a desire to disguise our decline from others. It may reflect a more general need to present a healthy face (and body) to potential mates or competitors - an extension of our use of cosmetics when younger.

Certainly, the social pressures are on us to look young. Laws are needed to prevent discrimination against older people. And stereotyping can again reinforce negative perceptions.

One argument is that negative attitudes emerged relatively recently, in the 18th century. Before then, elderly people were so rare they were held in high regard (only two per cent of the population in the late 1700s was over 65). But as they became more common, employers found they were holding on to jobs that younger, fitter people could do. Rather than being admired for their longevity, older people became a nuisance. This shift was reflected in the appearance of new words (e.g. codger), or shifts in meaning ('fogey', which originally meant a wounded war veteran).

Other social changes may have had an impact. In several countries, urbanisation has led to a decline in multi-generation families living together. Elders lose their social roles and are less valued.

It is often suggested that non-western cultures retain a greater regard for the elderly. In some African cultures, older people are revered because they hold their families' traditions through oral history. Yet negative stereotyping is common outside the west, and the social changes that drove attitudes in the industrialised world may now be spreading to developing nations.

And negative stereotypes are self-perpetuating. 'Old codgers' may be old codgers because they think they ought to be old codgers.