The shock of the old: Welcome to the elderly age

Of all the people in human history who ever reached the age of 65, half are alive now. Meanwhile, women around the world have half as many children as their mothers.

The longevity revolution affects every country, every community and almost every household. It promises to restructure the economy, reshape the family, redefine politics and even rearrange the geopolitical order over the coming century.

In most of Europe and much of east Asia, fertility is closer to one child per woman than two, way below long-term replacement levels. The notion that the populations of places such as Brazil and India will go on expanding looks misplaced: in fact, they could soon be contracting.

Tina Turner took to the stage in London, dancing in heels and a microskirt in her 70th year.

Millions of the middle-class retired continue working at everything from lucrative consultancies to teaching literacy or finally finishing that PhD. They are often more valuable than the young workers the demographers imagine are supporting them: in fact, the growing number of society's most qualified, most experienced individuals is potentially a huge demographic dividend.

This is sometimes called the Horndal effect, after a Swedish steel mill where productivity rose by 15 per cent as the workforce got older.

all the evidence is that "mass longevity facilitates affluence".