I'm walking very slowly down a little street in Shinagawa, trying not to get run over by the push chairs, and discovering all the things that I can't do anymore. I can't walk very fast because my knees don't bend properly, and an impatient queue forms behind me as I negotiate the ramp up to the 7-Eleven. I can't get the change out of my pocket either, and when the girl at the till tells me the price I can't hear what she's saying. I'm hot and irritable, and increasingly itchy. Just a minute . . . That's the last straw. I can't even pick my nose.

From the outside I look like a cross between a heavily-armored skate boarder and one of Darth Vader's storm troopers. Inside I feel the opposite: slow, heavy-limbed and vulnerable. A couple of kids suddenly whiz across my narrowed vision, nearly knocking me over. Young punks! When I was their age . . . In the last half hour I have come as close as you can to aging fifty years.

I am wearing something called the "Senior Simulator." It's described as a suit, but it's more like a collection of dastardly accessories, each designed to reproduce one of the effects of advanced old age. Plastic and velcro splints stiffen your ankles, knees and elbows. The pockets of the jacket contain weights which drag down your shoulders and back. You wear plugs in your ears, and goggles which dim and narrow your vision. There are three sets of gloves--skin-tight latex, then thick cotton to dull the touch (hence the nose-picking problem), and elastic to arthriticise the fingers. The parts are purpose-made by a surgical supplies company; an entire suit costs about Y300,000.

In Japanese the Simulator is called Taro Urashima, after a character from folklore, an unlucky cross between Rip Van Winkle and Dorian Gray. Urashima was a kind-hearted animal-loving fishermen who saved a turtle which was being tortured by a gang of kids. As a gesture of gratitude, the turtle took Taro to the submarine palace of the dragon queen. For three years, he had a whale of a time; when he left, the queen herself presented him with a jeweled box, with strict instructions never, ever to open it. Back on land, though, a century had passed--Taro's family, friends, and pets had long died. Understandably vexed, he opened the box, and was transformed in a moment into an old man.

It's an uncomfortably appropriate parable these days. As the twenty-first century approaches, Tokyo is becoming a Taro Urashima society. People here live longer than anywhere else in the world; at the same time, Japan has one of the lowest birth rates. By some estimates, more than a quarter of the population will be over 60 by the year 2000. "That means there will be fewer people to look after the elderly, and fewer taxpayers to pay for the cost of their social security," says Shukichi Gonjo, the inventor of the Senior Simulator and a full-time PR man for Tokyo Gas. "The government doesn't realize how serious it is, but it'll be a genuine crisis. In a few years, the pension system could collapse."

The obaa-san and ojii-san of the next decade, explains Gonjo, will be a different breed to the present generation of oldsters. The post-war boom broke up the traditional extended family, as children moved away to the cities. The economic miracle had another effect: many workers, mostly men, were robbed of any sense of leisure time. Hours were long, holidays were short, weekends were typically spent sleeping, golfing, and watching Beat Takeshi. "You get these men who have devoted their lives to their company, who have no hobbies, no idea of how to enjoy themselves," says Gonjo. "Their wives are lively; but they just lie down at home in front of the TV. We call them `wet leaves.' When leaves fall down they drift--as long as they're dry. But when they're wet, they just lie there, even when you brush them."

Gonjo's organization is called the Wonderful Aging Club, and one of its functions is to blow-dry the wet leaves. He organizes outings, meetings, and voluntary activities, the most popular job of which is acting as `instructor' on the Senior Simulator. Armed with the suits, gangs of WAC members pay visits to schools, companies, and government offices. They are hilarious occasions, as proud bucho are reduced to shambling octogenarians in front of their giggling subordinates. "But people are very moved, too," says Gonjo, "especially those who have elderly parents. We get letters from people saying that they feel guilty now about being so intolerant, that for the first time they understand what it's like to be old."

Taking off the suit will be great relief: I have been a horrible old man. Surprisingly, it's not the deafness or the immobility that are most alarming, but the isolation. I ask a question, and the people around us smile and wince, because I'm shouting, unable to judge the volume of my own voice. After that I whisper, but they keep having to repeat the answers, so my colleagues ask the questions on my behalf. I may be a bit of a wreck, I want to say, but between the ears I'm still as sharp as a razor. But someone else is conducting my interview, and writing in my notebook. I sit at the side, ignored.