From the mountain trails of Hokkaido to the six-lane expressways of Shikoku, a fearsome clique of tearaways has emerged to terrorise Japan’s roads: leather-clad, rebellious and with a touch of lumbago.

These are the country’s “mature riders”; the creaking ex-salarymen — and their molls — who built the Japanese economic miracle. Retired, bored, pushing 70 and with a hankering for the wayward youth they probably never had, they are the last hope for Japan’s motorcycle market.

Many of the new breed of grey-haired bikers are mounting their hogs in the belief that the activity will stimulate their brains and stave off senile dementia. Those who, decades earlier, swapped their dreams of the open road for employment, marriage and parenthood are being encouraged to retrain as “return riders” in specially organised refresher courses. Those starting from scratch are termed “late riders”, with leather-jacket rentals and discount-group rates gently encouraging them to form gangs.

The phenomenon has not developed entirely independently, but is the result of a marketing lunge by the increasingly desperate bike makers. Yamaha, in particular, faced with plummeting domestic sales — down from 3.2 million bikes in 1982 to less than one sixth of that now — has enticed the country’s burgeoning older generation on to saddle and pillion.

At this month’s Tokyo Motor Show, Yamaha intends to unveil its first hog designed entirely with the elderly rider in mind. “Surely people will see this and think back to the time when they loved the idea of motorbikes,” said its designer.

The bike features functions that supposedly compensate for ageing reflexes. Honda has produced a large automatic bike for the first time in 30 years, with the same market in mind. Kawasaki has re-engineered its Ninja line so that the seats are lower and easier for the elderly to mount.

Ryuta Kawashima, who developed Nintendo’s popular Brain Training game, can also take credit for the trend. In what is referred to as a piece of “industry-academia research” — it was funded by Yamaha — Professor Kawashima’s team attached probes to bikers’ heads and surveyed their brain activities as they rode around. “Incorporating motorcycle riding into daily life improves cognitive functions (particularly prefrontal cortex function) and has positive effects on mental and emotional health,” was the conclusion.

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