When it comes to running marathons, eight hours, 25 minutes and 16 seconds is not a world record.

This was the time it took Fauja Singh to complete the Toronto Waterfront Marathon on Sunday.

But Singh, born in India, is no spring chicken – he's 100 years old and his recent feat has made him the world's oldest marathon runner.

As an athlete, Singh was a late starter. In his late 80s, after the deaths of his wife and son, he decided he was not yet over the hill and took up running.

For Singh, being 100 is just a number. There aren't many centenarians in quite such rude health, but they are on the increase. Life expectancy in the UK today is around 80 but a total of 12,640 men and women are now centenarians compared with just 2,500 in 1980, according to official statistics.

In Britain, pensioners that reach this landmark age receive a congratulatory telegram from the Queen, herself an 86-year-old senior citizen.

Retailers and public services are having to adapt to this aging society. New figures reveal the amount of money spent annually by people over 65 in the UK is nearing the 100 billion pounds (1 trillion yuan) mark. A whole sector of the economy is now catering to the needs of the grey pound.

Why do some people live to such a ripe old age? Scientists in Amsterdam may have come a little closer to discovering the secret to longevity; they've encoded the entire DNA sequence of a woman who lived to 115.

Of course, they could just ask Fauja Singh what his secret is. The old boy puts his long life down to ginger curry, tea and "being happy".