GU BIN leans over a desk as he carefully adds strokes to the Chinese character for "fortune", before signing off in a flourish with his age 104.

But the spry great-grandfather is five years younger than the oldest member of the community in Rugao, an eastern city home to more than 500 centenarians and which celebrates its elderly with pride, statues and subsidies.

Calligraphy is one of the many hobbies practised by Gu, who was already in his nineties when he taught himself to use the internet.

"I write poetry, read books and newspapers, and watch the news every day," says Gu, who was born in 1918, in the tumultuous early years of China's republican era.

Decades of a one-child policy has built in a demographic challenge for China, with a low birth rate and the world's largest population of elderly to provide for, while the pressure of urban life is ripping up traditions of filial responsibility for aged parents.

By 2050, the government predicts retirees will constitute a third of China's population and caring for them will cost a quarter of annual GDP.

This week's census data showed China's population over 60 had reached more than 264 million a five percent increase over the last decade making Rugao a testing ground for the country's future.

It is dubbed China's "longevity city" for its impressive number of super seniors, with 78,000 people aged between 80 and 99 among its 1.4 million residents and another 525 over 100.

Temples and parks are replete with the elderly praying with longs sticks of incense, dancing or practising the slow strokes of tai chi.

Older residents gather to chat on cobbled riverside streets, or sit in public squares to sing songs in a city which celebrates its pensioners with a 50-metre tall statue of Shouxing, the God of Longevity.

"Our ethos here is to respect the elderly," Rugao Longevity Research Centre director She Minggao -- who is nearly 70 years old himself -- told AFP.

"We believe that to have an elderly person in a family is like having a treasure."

That pride reflects onto the residents. Gu shows off a heavy medal for city centenarians who complete a hundred-metre walk, as well a certificate dated 1951 for fighting in China's People's Liberation Army.

Bundled up in padded trousers, coat and hat, the former accountant mostly stays home after a fall a few years ago.

But he maintains his sharp wit and keeps connected with the outside world through the internet.

"Biden is just too old to be president," Gu quips, pointing to a news item about the 78-year-old US leader.

"He's not as old as me, but he's also not as smart."


Work ethic

Rugao around 200 kilometres from Shanghai is surrounded by fields of green and yellow crops and decorated with stately canals. Locals believe the natural environment has a part to play in their longevity.

Researchers from the Chinese Academy of Sciences speculated in one report that high levels of the mineral selenium in the city's soil could be a factor extending the life expectancy of its citizens.

But after over a century living through China's tumultuous history, others have a more straightforward explanation.

"I still work," says great-grandfather Yu Fuxi, aged 103, who zips around town on his motor scooter.

"I sweep the floor every day and like everything clean and tidy. I go to the market on my scooter and buy what I want," he adds, from a room with a neatly rolled up bedspread and picture of Chinese president Xi Jinping on the wall.

Yu regularly makes meals for his grandchildren, darting around the kitchen in white cooking overalls.

Across town, Qian Zuhua -- two years his junior -- is equally motivated helping at his son's screw production factory, matching metal nuts and bolts with his still nimble fingers.

"I'm 101 and my health is good," he told AFP from an apartment shared with his son, grandson and great-granddaughter.

"I am happy when I think about it."


Empty nesters

The elderly in China are traditionally cared for at home by younger relatives.

But the one-child policy created a fast-ageing population and a shrinking workforce, putting pressure on working children to care for two sets of parents.

Urbanisation, long working hours and high property prices plus changing mindsets among many younger, cosmopolitan Chinese makes pairing tradition with modernity a challenge.

Rugao authorities introduced subsidised or free door-to-door services health checks, hair cuts and massage for the elderly.

Residents also get a pension top-up that increases with age, and a subsidy towards elderly care costs.

But in other parts of China, elderly care is less expansive.

"Government-run institutions are in high demand and typically have long waiting lists," said Kyle Freeman, partner at consultant Dezan Shira and Associates.

In contrast, he says, expensive private facilities are mostly below capacity.

With many families now made up of one child, two adult parents, and four elderly grandparents, Chinese children are being squeezed as they try to care for relatives.

"My son is working in Beijing, so we are the empty nesters," said Wang Yingmei, 85, from the tidy room she shares with her husband in one Rugao elderly care home.

"It's actually more cosy than our home, because there is nobody else at home but us."


Price of getting old

Residents pay around 4,000 yuan ($600) a month for their room at the centre.

That is roughly the average monthly income of a city resident in China -- but more than double the income of a rural worker.

Freeman says elderly care could overtake real estate as China's largest industry within the next fifteen years, with health officials projecting total elderly care costs could go from about seven percent of GDP to more than a quarter by 2050.

Chinese policy aims for 90 percent of the country's elderly to be cared for at home, but to achieve that authorities will need to stir a change in mindset.

"The implication is a return to filial piety in China which took a break, particularly in cities, over the last 30 years," said Sofya Bakhta, a China market analyst at Daxue Consulting.

Gu Bin is quite content at home in his leafy apartment where he knows his neighbours, lives with his daughter and son-in-law, and can indulge his flurry of newly-found hobbies.

"In the past China was poor, we owned nothing. Now I have a place to live, food to eat and my clothes are warm.

"Life is good."