Entrepreneurs are exploring robotics and other innovations to unleash the potential of the elderly.

At an office-building construction site in the center of Japan’s capital, 67-year-old Kenichi Saito effortlessly stacks 44-pound boards with the ease of a man half his age. His secret: a bendable exoskeleton hugging his waist and thighs, with sensors attached to his skin. The sensors detect when Mr. Saito’s muscles start to move and direct the machine to support his motion, cutting his load’s effective weight by 18 pounds. “I can carry as much as I did 10 years ago,” says the hard-hatted Mr. Saito. Mr. Saito is part of an experiment by Obayashi Corp. , the construction giant handling the building project, to confront one of the biggest problems facing the company and the country: a chronic labor shortage resulting from a rapidly aging population. The exoskeleton has allowed Mr. Saito to extend his working life—and Obayashi to keep building.

Conventional wisdom says a large elderly population undermines an economy, and that Japan’s unprecedented aging condemns the country to a bleak future. The logic: Old people are an unproductive drain, squandering resources on pensions and health care, while doing little for growth through working, earning, spending or paying taxes. One in four Japanese is 65 or older, compared with 15% in the U.S. There are now just 1.6 working-age Japanese available to support each senior or child under 15. That ratio is already considered unsustainably low. By 2050, there will be just one working-age Japanese for every senior or child. During the high-growth 1980s, Japan had more than two, about the same as the current U.S. level.

Pessimists say the only way to keep Japan from inexorably drifting into bankruptcy is radical change, like a sudden, sharp influx of immigrants—an unlikely prospect given Japan’s history as one of the world’s most homogeneous cultures.

But a growing number of Japanese executives, policy makers and academics challenge that proposition. They are exploring whether modest adaptations can ease the woes of an aging society, or even turn the burdens into benefits. The optimists’ case starts with steering the growing number of healthy 60- and 70-year-olds from retirement into work. That makes them more productive members of society while helping staff jobs that otherwise would be impossible to fill as the population shrinks.

“We have to change our view from ‘antiaging’ to ‘smart aging,’ ” says business consultant Hiroyuki Murata, author of Japanese best-sellers like “The Business of Aging: 10 Successful Strategies for a Diverse Market.”

Japan’s life expectancy is 87 years for women, the world’s longest, and five years more than in the U.S. For men, it is 81—the third-longest in the world, and four years greater than in the U.S. Japan’s “healthy life expectancy”—an estimate of the age a person can reach and still live independently—is the world’s longest for both women (75) and men (71), according to a study published in the Lancet, a medical-research journal.

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