Peter Smith, dean of medicine at the University of NSW, said a girl born today in Australia could reasonably expect to live to 100 already, due to advances in medicine, lifestyle and public health.

Also, new drugs to help the body repair itself were in the early stages of development, along with new stem cell therapies.

''I think there is real hope we can extend human life by some decades further,'' Professor Smith said.

Living to 150 may sound unnerving, but it would be ''great'' if you were well until near the end, he said. ''The aim is not just to eke out extra existence but to facilitate a longer healthy life.''

Such longevity, however, would raise serious issues for society, which are the subject of the UNSW Medicine Dean's lecture tonight, titled Happy and healthy ageing: paradox or possibility?

''People aren't going to want to retire at 65 and spend many, many decades sitting at home,'' Professor Smith said.

Baroness Susan Greenfield, a neuroscientist at Oxford University, also foresees people starting second careers at 65, in knowledge-based jobs, rather than physical ones.

But she said tackling dementia, which includes Alzheimer's disease, needed to be a priority. ''Otherwise the social and economic implications could potentially be catastrophic.''

David Sinclair, an Australian expert in ageing at Harvard University, said a network of genes controlled the pace of ageing. ''Our bodies have an extraordinary ability to repair themselves.''

Professor Sinclair has shown that resveratrol, a plant compound found in red wine, can extend the lifespan of yeast, worms, fruit flies and fat mice, by activating proteins called sirtuins.

The company he co-founded was bought by GlaxoSmithKline for $US720 million in 2008.

Clinical trials of synthetic molecules 1000 times more potent than resveratrol are under way in people with diseases of ageing, such as diabetes 2, he said. ''And [they] are showing early signs of efficacy.''

The immediate aim was to find medicines to treat elderly sick people, then later attempt to delay the onset of diseases of ageing. It was still very early days, he cautioned. But ''I think we're seeing the beginning of technology that could one day allow us to reach 150'', he said.

British scientists last month challenged the link between sirtuins and longevity in worms and fruit flies in the journal Nature.

Professor Sinclair said ageing was still ''one of the most controversial areas of science'', but he was confident his team's research was soundly based.