Japan used to follow a wonderful practice to mark old age: Everyone who reached their 100th birthday received a silver sake cup called a sakazuki. It’s certainly better than the tradition in Britain, where centenarians simply get a letter from the queen.

The sakazuki gift was a nice idea when it was introduced in 1963. Back then, there was a certain rarity to it, as there were only 153 centenarians in the entire country.

However, life expectancy has been increasing rapidly and Japanese in particular have started living longer. So many centenarians celebrated their 100th birthday in 2014 that an astonishing 29,350 sakazuki were sent out. It was getting out of hand. In 2015, the custom was cancelled. It’s just not unusual to reach 100 anymore.

We hear a lot about Japan’s graying society, mostly centered around concerns about how the country is going to cope with so many elderly people. Already 1 in 4 Japanese is aged 65 or older, and the number of elderly people is increasing.

However, here’s a fact that cuts through the usual concerns: A child born in Japan today has more than a 50 percent chance of living to be 107.

One hundred and seven! We might be dimly aware that we will have to work for longer than our parents, but most of the implications of the extraordinary increase in human lifespan have yet to be addressed. Lifespan has been increasing by three months a year since 1840. We need to start thinking about what to do about it — not just how to care for the elderly, but on a personal level. We need to start making plans for our own long lives.

This is the subject of a new book by Lynda Gratton and Andrew Scott, a pair of British academics at the London Business School. In “The 100-year Life” they consider the ways in which we should change our outlook on life to adjust for the fact that we are living for so much longer.

There’s a well-known cognitive experiment that has people describe what they wish they’d known when they were younger.

Gratton and Scott turn this cognitive experiment around. Instead of examining what you would say to your younger self, ask yourself what your older self might say to you. What advice might your 80- or 100-year-old self give you now?

The idea is to bring home the importance of the revolution in lifespans we are all experiencing. We won’t be able to retire at 60 or 65 like our parents did. We’re going to live longer, so will need to save more money into our pensions before we stop working, probably (hopefully!) around 80.

The younger generation will live even longer. Currently we think of life as having three main stages: education, work and retirement. However, we need to think of life as having multiple stages, perhaps with different periods of education to stay relevant and engaged with society as we get older.

Gratton and Scott argue that rather than thinking of people being older for longer, we need to think about being younger for longer. They call this “juvenescence,” or the state of being youthful or staying young.

It’s important to reframe our thinking in this way. Some of the problems our society faces today are that older people may be isolated, lonely and unfulfilled. By planning and altering the choices we make and the paths we follow as we age, we can help ensure that when we get older we are in a better place mentally and physically.

Another serious concern, highlighted by the Nippon Institute for Research Advancement, is that as the population gets older, voters vote for policies skewed to their needs. Some 47 percent of voters in the country’s Upper House election in 2010 were 60 or older. The needs of elderly people are, of course, vital but the needs of the young shouldn’t be neglected. The National Institute for Research Advancement has warned that the bias toward older people will place a heavier burden on younger people.

All this research is good. We are recognizing the problems, even if we don’t yet have solutions. We are also learning more about the genetics of longevity. An obvious way to investigate this is to study centenarians, so gerontologists — scientists who study aging — go to places where there is an above-average lifespan, such as the island of Sardinia in Italy, and Okinawa in Japan.

A study published in the Journals of Gerontology: Series A found the Okinawan genome to be strongly linked to extreme longevity. In one study of 348 Okinawan centenarians born between 1874 and 1902, and 969 of their siblings, researchers were able to determine that there was a stronger genetic component to their old age than has been found in Caucasian centenarians.

In centenarians in general, scientists have conducted what are called genome-wide association studies. This is a statistical test that determines which genes are linked to longevity in a person. Genome-wide association studies show that centenarians tend to lack genes linked to a number of diseases, in comparison with the general population.

The spirit of juvenescence is probably best represented by an old saying in Okinawa, which is the poorest prefecture but the one with the longest-lived people.

“At 70, you are still a child,” so the saying goes. “At 80, a young man or woman. If, at 90, someone from heaven invites you over, tell them to go away and come back when you’re 100.”

Maybe the saying needs updating: “If, at 100, someone from heaven comes for you, tell them to go away and come back when you’re 110.”

And bring a sakazuki bowl.

Rowan Hooper is the news editor of New Scientist magazine.

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