London - Life expectancy at birth could reach 100 in the next 60 years if present trends continue.
While for today's population living to be 100 is an achievement, in two generations it could be as routine as collecting a bus pass, scientists write in the Journal of Epidemiology and Community Health.
A study of the growth in longevity in Switzerland has revealed that more people live to be 100 there than anywhere else in Europe.
In 2000 there were 796 people aged 100 or older in Switzerland and the number has doubled every decade since 1950.
Worldwide, life expectancy has more than doubled over the past 200 years - from 25 to 65 for men and to 70 for women in developed countries.
Switzerland has some of the highest numbers of "old old" - 90 or over - according to analysis of census, population and death statistics for 1860 to 2001.
The Faculty of Biology and Medicine of Lausanne found that apart from a dip in 1918, the year of the flu pandemic that killed millions worldwide, life expectancy rose by 98 percent for men and 96 percent for women.
The emergence of the extremely old population has happened only in the last 50 years and is chiefly due to improvements in the health of the elderly.
The 1950s were a crucial period for the development of the oldest old in other countries, such as France, which still holds the record for the world's oldest person, who died in 1997 aged 122.
A study in Sweden found death rates among people aged 90-94 over the period 1861 to 1999 were directly related to their wealth as measured by manufacturing wages.
In England and Wales there were 6 000 centenarians in 2001.