Japanese super granny, still an active swimmer at 99..Waoh

(CNN) -- Despite being an 18-time world-record holder, Japanese swimmer Mieko Nagaoka is determined to win more medals and break more world records.

But Nagaoka is not your average ambitious sportswoman. She is 99 years old and only took up swimming when she was in her early 80s.

"I don't care about my age," says Nagaoka. "I can't believe I'm 99. I still feel I like challenging everything."

Her coach is also full of praise for Nagaoka, saying she is "the type who just doesn't want to be defeated and is strongly determined to win more gold medals, world records.

Nagaoka is among a growing number of elderly Japanese who not only challenge but also shatter stereotypes of what aging means in the country.

Japan's demographic crisis is well-known: around one quarter of the Japanese population -- 31.86 million -- are 65 or older, according to government figures published in September, a record high. It is estimated there are over 54,000 centenarians, a 6% increase from 2012.

With the world's longest life expectancy (84 years), and one of the lowest birthrates, Japan is expected to see sales of adult diapers overtake those of baby diapers by 2020.

However not all senior citizens are enjoying retirement. With 1 in 5 senior citizens employed, according to the Statistics Bureau of Japan, the country has the highest proportion of working seniors in the developed world. Financial necessities and boredom are among the most commonly cited reasons.

But even if they don't have to work for a living, many elderly Japanese don't want to live in isolation. Though not all can replicate the active achievements of Mieko Nagaoka, many senior citizens still have enough energy to spare or keep an active social life.

Take for example, the Pom Pom Grannies, a cheerleading squad with an average age of 67. The routines are not just a physical exercise, according to the 81-year-old founder Fumie Takino, but help keep one's mind sharp as well.

In an attempt to deal with swelling pension costs, Japan is gradually raising the retirement age to 65, from 60 last year.

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