Why do some people live to 100?

Exceptional longevity - living to 100 - is about 70 percent due to genetics and 30 percent due to lifestyle, says Professor Thomas Perls, founder of the world’s biggest study of centenarians.

Understanding their genetic resilience to age-related diseases will eventually lead to the development of drugs, he says, but right now, our best strategy for ageing well is committing to healthy habits.

“The benefits of this are going to be far greater than some drug that we're going to come up with," Perls tells Saturday Morning.

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When Perls launched the New England Centenarian Study in 1994, he says the general assumption was that the older we get, the sicker we get.

But he soon realised that not every centenarian has “every disease under the sun” and some are still “doing very, very well” in their second century of life.

When it comes to healthy ageing, centenarians “raise the bar”, Perls says.

“People who run marathons make the rest of us think that running a 10k race is doable. That's what [centenarians] do for us.”

Obviously, socio-economic and racial disparities mean not everyone is well set up to live a long, healthy life.

Perls sees this clearly in Boston, where the affluent Back Bay area has an average life expectancy of 93 years, but just 5km away in poverty-stricken Blue Hill, it's 23 years less.

When it comes to a genetic inheritance of longevity, having just one parent who lived a long time is enough to boost your chances of a long life, Perls says.

People can inherit from a family member a not-yet-understood collection of genes that are “protective” in being effective at DNA repair.

“[These genes] slow ageing and they decrease your risk for age-related diseases and decrease your risk for Alzheimer's disease.”

Even people without this genetic gift have "a very good shot" at reaching 93 if they do the right things, Perls says - regularly exercise their brain and body, eat a diet "conducive to a healthy weight", don't smoke and keep an optimistic attitude.

He summarises the factors that contribute to ageing well with the acronym AGEING - Attitude, Genetics, Exercise, Interest, Nutrition and Getting rid of smoking.

A big reason Perls "really loves" pushing the idea that healthy habits can help people live to 93 is that these same habits will help them stay healthier for longer.

Pushing back the onset of age-related diseases is a real incentive to take better care of ourselves, he says, and to help encourage mass behaviour change, public education and funding would be beneficial.

“The benefits of that, I think, are going to be far greater than some drug that we're going to come up with.”

While today's centenarians are usually very optimistic by nature, many are also “a bit dismayed" by our tech-driven culture and the ongoing threat of war, Perls says.

“They harken back to a simpler life - a life where people interacted with each other face to face, rather than at high speed on the internet.”

At 65, the professor is still keen to get to three figures himself.

He's doing all of the recommended things and may have some genetic assistance from his mum, who made it to 96.

“I might have a chance to get to 100, particularly if I take good care of myself.”

Watch videos of participants in the New England Centenarian study here.