By Branwen Jeffreys
Health correspondent, BBC News
Matsu Yamazaki remains very active
Each day Matsu Yamazaki steps out of her small house in a Tokyo suburb to walk through busy streets to work at her family's grocery shop.
It would be unremarkable but for the fact she is 103 years old.
Mrs Yamazaki has survived an earthquake that devastated Toyko, the second world war and cancer in her seventies.
She cooks and cleans for herself, keeps her hands nimble through crafts and her mind agile through mathematic puzzles.
This is how we imagine old age in Japan, remarkably healthy and active.
"Even if I go on living, I just don't want to lose my mind," she said.
"I know lots of people who've lost their memory. They go out and wander around town and can't find their way home. "
Pensioner numbers growing
For Japan that is the problem - by 2055 the government is predicting pensioners will be around half the population.
The numbers of the very oldest are growing steeply and that means rising costs.
A look at around a care home in Japan
Already caring for the elderly accounts for half of the health budget, and Japan has a huge financial deficit.
So long term care insurance for the elderly was introduced in 2000 to help shift care out of hospitals.
The contributions are raised from the working population over the age of 40.
Some changes were added in 2006, including incentives to promote more independent living at home.
Much more controversially a new health insurance scheme for the over-75s was introduced this year.
Elderly patients told me they do not like being singled out and issued with special cards.
It has already been nicknamed the 'hurry up and die' scheme, and has whipped up a political storm.
Fee goes down
In Hotano city an hour from Tokyo Dr Jun Saiwadaishi showed me around the wards and rehabilitation units of the hospital where he works.
Under recent changes the fee the hospital receives for a patient goes down after 100 days - as an incentive to shorten hospital admissions which are long by international standards.
Dr Saiwadaishi has launched a human rights legal case against the government because he is so angry.
"If we just go ahead and cut budgets - Japan should be ashamed of that internationally.
"I think it is really dreadful - nothing like this has ever happened."
A few days later in a publicly run care home in a wealthy part of Tokyo I saw the other side of old age in Japan.
Volunteers from the neighbourhood had come in to sing folk songs with the residents, most of whom have dementia.
The words are too hard to recall for many, but almost all added a faint voice to the song.
Just under a third of Japanese people over the age of 85 have Alzheimer's or some other kind of dementia, a very similar rate to the UK.
So the increase in the very oldest has created unprecedented pressures.
Under the long term care insurance elderly people here contribute 10% towards their care and demand for places has increased.
Matsu Yamazaki on her wedding day
There has been an increase in the number of nursing homes but not enough.
At just this one home there are hundreds of people on the waiting list.
One floor of the home is unused because of staff shortages.
Local companies can offer better pay for easier work.
The manager Masae Tanaka told me he has to turn away families desperate for a night of respite care.
"The families tell me they can't cope looking after them at home, they're exhausted and plead with me to take their elderly in.
"They'll go under as well with the strain of it all. In Japan this is called a double collapse."
Like some of the doctors I met he is pessimistic about the ability of the system to cope as the population continues to age.
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But many experts support the government's efforts to find solutions which are financially sustainable in the long term.
Trying to introduce measures which ask people to pay an increased contribution is politically tough.
One of Japan's leading health economists, Professor Naoki Ikegami argues their long term insurance has been a success by widening access to social care.
He still believes there are hard choices ahead: "politicians don't like making unpopular decisions and raising taxes or cutting benefits is unpopular but they have to make either of these decisions. "
The growing proportion of the elderly are a significant political influence in Japan.
No party can afford to ignore their votes.
That may mean that younger generations face more radical reforms as it is easier to adjust entitlement with several decades warning.
The dilemmas faced by Japan now lie ahead for all the major economies whose populations are also ageing.
A rapid growth in the very oldest can create a heavy burden for families, and a financial headache for governments. In Japan, as in parts of the UK, the debate is how the burden should be shared.