The research shows that there appears to be no fixed upper limit to our lifespans and that once we live beyond a certain age, perhaps 85, we could well survive to see a telegram from the Queen.
According to a team of scientists in the US, the fly experiments suggest that by the middle of the next century the number of people in the West over 85 could increase from today's 1 per cent to 15 per cent or 20 per cent, putting enormous strains on welfare in countries already braced for ageing populations.
'The notion that there's some fixed limit to a person's life, which you inherit from your parents, is overly simple,' according to Dr James Vaupel, who researches into ageing at Odense University in Denmark and was a member of the American team that carried out the fly research.
'Given current knowledge, if people began following good health practices today, they might live 90 years or even 100 years, on average.'
Life expectancy at present is about 75 for most western countries, but is already increasing owing to better housing, diet and health care.
The research, published in the latest issue of the journal Science, shows that a central tenet of biology and the life insurance business - that death rates accelerate as people get older - is not true, at least for flies.
The belief in an accelerating death rate is enshrined in 'Gompertz's law', proposed in 1825 by Benjamin Gompertz, a British actuary. The law implies that death rates climb dramatically in old age, effectively putting a cap on lifespan.
However, Dr Vaupel and colleagues from the University of California, University of Minnesota and Duke University, North Carolina, demonstrated that beyond a certain advanced age, death rates slow down in a population of more than a million flies, with the oldest flies living progressively longer.
Dr Vaupel said the results could be applied to humans because the basic genetic functions of flies and man are similar. 'These studies are changing how we think about the survival of people at very advanced ages.'
The research does not mean that humans 'are going to live to be 999 years starting tomorrow', he said. 'It does mean that life expectancy, which in the US is about 75 years, could be significantly increased.'Reuse content