"If I last that long," he said with a chuckle.

Mr Torok is one of four centenarians living at the St Elizabeth Home in Dean Park, in Sydney's west, where two other residents are set to mark their 100th birthdays this year.

Centenarians used to be rarities, featuring in the news as they read their congratulatory letter from the Queen. There were about 120 in Australia in 1975.

But more people are living longer. ABS figures show that in the year to June 2016, another 600 Australians marked their 100th birthdays, taking the number of centenarians to 4870 – three-quarters of them women. On current projections there will be an estimated 41,100 of them by 2050.

The Guinness World Record for the largest gathering of centenarians was broken in November, when 45 attended a lunch in Brisbane hosted by Queensland Premier Annastacia Palaszczuk.

The month before, an unofficial record was set when 57 centenarians attended the sixth Century Club celebration at Government House in Melbourne.

Former Victorian MP Donna Bauer organised the inaugural Century Club gathering after realising "we had six or seven centenarians living locally".

"Reaching 100 is such an incredible milestone, so worth celebrating," she said. "For other centenarians to meet people born in the same year is just so valuable for them. They're full of positivity, great advice, always love sharing their secrets to longevity."

Asked what helped him reach such an impressive age, Mr Torok mentioned his loving family and keeping mentally and physically active.

"You have to be not overdoing things, but always doing something," said Mr Torok, who lives at the .

A Hungarian-born retired carpenter, Mr Torok lives in the villa at the St Elizabeth Home that he shared with his late wife, Piroska. He only recently gave up driving.

"I have a heart condition which restricts me to a very slow type of life," he said. "I used to go to libraries, museums, exhibitions in the city. Reading is my main occupation, besides cooking and cleaning.

"I am still interested in what's happening around the world. I know that I am out of the way and I don't know – it might be the next morning I'm not here. But still I am interested in it."

People always tell him he is exceptional for his age "but I think it's getting much too long", Mr Torok said. "The system is all used up."

Researchers have examined which factors determine who reaches triple figures, with genetics, lifestyle and diet playing a part.

Blue zones – areas noted for the exceptional longevity of the residents – have been identified in Costa Rica, Sardinia, the Greek island of Ikaria and Okinawa in Japan. Those communities prioritise family and are socially engaged. They tend not to smoke, have diets high in vegetables and legumes and enjoy constant moderate physical activity.

Researchers at UNSW's Centre for Healthy Brain Ageing examined the determinants of successful ageing during the Sydney Centenarian Study, which recruited 345 people aged between 95 and 106.

While 55 per cent of participants met the criteria for dementia, 20 per cent had no problems with their physical or mental functioning and about half were still living independently in the community, CHeBA co-director Perminder Sachdev​ said.

"One important finding was that these individuals have often been very healthy until a very late age," he said. "If they have diseases such as hypertension, coronary artery disease, diabetes, often these are late in developing, so somehow they've been able to push back [these diseases] – and some have been able to avoid it altogether."

Those who avoided disease were probably "genetically blessed", Professor Sachdev said, while those with delayed onset of disease "have had good lifestyles".

"The seeds for healthy old age are sown very early in life with good education," he said. "[Achieving] healthy old age is actually a lifelong enterprise. You're really looking at your risk factors, your diet, your weight, your exercise, cognitive activity."

Along with research by former La Trobe University lecturer John McCormack, who interviewed 130 centenarians, the study helps dispel assumptions that anyone living to such an old age will inevitably be dependent on aged care and public health services.

"It's a negative stereotype that anyone at that age is decrepit, almost in a vegetative state, in a nursing home," Dr McCormack said.

He found a history of physical work and not being overweight were the most common characteristics among centenarians and that, having lived through war and the Depression, they were very resilient.

"They focus on what they can do, rather than what they can't do," he said. "Doing things in moderation is one of the lessons they've learned."

But as the ranks of octogenarians, nonagenarians and centenarians continue to swell, government, businesses and society will have to adapt, John Piggott, the director of the ARC Centre for Excellence in Population Ageing Research, said.

Workplaces will have to more readily accommodate older workers, access to the age pension will need to be expanded and "the tax take will have to go up in the long-term", Professor Piggott said.

"It's a positive thing, not a negative thing, that we're living so much longer than we used to," he said. "But we haven't had this happen before, so there is the issue of how well we adjust."