Statistics tell us that the average Japanese life span, for both men and women, is the longest in the world. But this does not mean that almost all Japanese live long lives. One reason for the high percentage of elderly people is the country's low birth rate. The infant mortality rate is low, too, and this is another factor extending the average life span. So we cannot say that almost everyone in Japan will live to be very old.

It is true, however, that 40 years ago Japan had only about 100 centenarians, while today there are more than 20,000. At this rate, the number will probably climb above 30,000 within a few years.

The most important reason for longer contemporary life spans is diet. Those who are now 60 or older were born before the war, at a time when people ate more sparingly, and even today most of them do not eat heavy meals. If you restrict calorie and cholesterol intake, you will have less hardening of the arteries, which is a major cause of illness.

People who live long have a number of things in common. For one thing, almost none of them are overweight. Obesity puts stress on the heart and increases the possibility of hardening of the arteries. It is important to have a fairly high calorie intake when you are young, but after the age of 60 you should be careful about calories and cut back on animal fat, which contains high amounts of cholesterol.

During the Edo period in Japan, there was a Confucian scholar named Kaibara Ekiken (1630-1714) who wrote A Manual for Healthy Living (Yojokun). Kaibara said that one way to stay healthy is to stop eating when the stomach is about 80% full. I would say 70% is even better. To stay healthy, eat just enough to stay within the desirable weight range. But that does not mean you should eat only vegetables or avoid things you like. It is OK to eat some meat and fish for an active life. The important thing is to keep calorie intake down and to cut down on animal fat and sugar.

We have to exercise to burn off calories. I will be 93 soon, but I still avoid escalators at stations and airports. I take the stairs and carry my own luggage. As you age, it becomes more difficult to move your joints, so you need exercise to keep them flexible. If you cannot manipulate your joints properly you will not want to move about, and that will reduce your chances of interacting with other people. Exercise is very important, and a physically and mentally inactive life could lead to dementia.

Very elderly people are keen to monitor their physical condition, checking for possible symptoms of disease. Even if you think you have no symptoms, have a checkup once a year, so that any problem can be detected and treated in the early stages. When we detect cancer or an ailment that could, for example, lead to a heart attack, we can increase the survival rate.

The most important factor is one's outlook on life. Be optimistic. Do what you want to do. For example, people might worry if they did not get a good night's sleep, but generally, not being able to sleep is not a major problem in itself—the problem is worrying about it.

There are all kinds of theories, like "Early to bed, early to rise,"or "Eat three good meals a day." But people with a zest for life remain healthy even if the natural rhythm of their day is a little upset sometimes. About once a week, I work into the wee hours. If I have a big writing job and the deadline is approaching, there might be one night when I have to work really late, but I feel good about it all. If I write something I am proud of, I feel great, even if it took me all night. At the hospital I am affiliated with, I see staff members who look dog-tired after the night shift, but that is because they resented their obligation to keep working. Just because you are not able to sleep does not mean you cannot enjoy what you are doing.

When you become old, life moves in one direction or another, depending on whether or not you have strong interests and are pursuing them. It would be a big mistake to think, "When I'm old, I'm going to take it easy." It is better to keep active at things you like doing. Interacting with people, living a stimulating life—those are the kinds of things that keep you going.

But there is less point in living long if you are bedridden or if you withdraw from the active world. It is important that elderly people remain independent and keep socially active. The retirement age is 60 at many Japanese companies, and that is when employees generally retire. But the age 60 rule was set years ago when the average life span was 68. Today, the average life span in Japan is more than 80, so I think people should be able to keep their jobs until 70.

I started the "New Old People's Movement" for seniors over 75. The human body contains about 36,000 different genes, and there are many genes people do not take advantage of. The movement stresses that we can use the potential of some of those genes to do things we have never tried before—music, painting, sports, whatever. It does not matter if there is no financial reward. Enjoying new experiences and staying active in body and mind keeps elderly people healthy and happy.

Almost 19% of the Japanese population is 65 or older. Statistics indicate that the percentage will increase to 25% a quarter century from now. For society's sake, too, we need to have more "new old people" living life to the full.