Washington is abuzz over the politics of work. Will ObamaCare create jobs or destroy them? What would raising the minimum wage do to youth unemployment? And what to do about the long-term unemployed? Yet there is an odd political silence about a future vision for jobs and economic growth.

One vital question in particular goes largely unaddressed: How do we build an economic growth model for an aging society? As the over-60 population grows much faster than the younger working-age cohorts, while life expectancy increases, the 20th-century model of work and retirement becomes increasingly unsuitable for economic growth. The key will be finding new solutions to engage older Americans in the workforce.

With declining birthrates throughout much of the world, humanity is getting older. In Europe, the median age has climbed to 43 over the past 30 years, from 34, while in Japan-with the oldest population on the planet-the average age is 46, up from 39 in 1994. The American population is aging too (median age: just under 38), though more slowly thanks to immigration and a relatively high birthrate (almost two births per woman, in contrast to Japan’s 1.2-1.4). But this won’t last forever. The U.S. should adapt now or risk being less prosperous and competitive in the 21st century.

Research suggests that keeping older workers engaged in the economy will directly boost gross domestic product. In Japan, a 2005 study by the Nihon University Population Research Institute concluded that increasing the retirement age to 65 from 60 could raise per capita GDP 10% by 2025.

Calculations by the U.K.’s International Longevity Centre earlier this year suggest that increasing the total number of workers over 65 by just 2.6% a year could boost per capita output in 2037 by as much as 6%, cumulatively adding nearly £1.7 trillion to the U.K. economy-more than total British GDP today. Those estimates don’t take into account benefits from a longer work life to national wealth, budgets or public debt.

There is also mounting evidence that working later into life correlates with better individual health and satisfaction, and may contribute to them. Amid skyrocketing age-related health-care costs, this advantage can scarcely be overstated. Research by the Department of Work and Pensions in the U.K. found in 2006 that recipients of age-related entitlements “who move off benefits and re-enter work generally experience improvements in . . . mental and general health, and well-being.”

Thus at all levels of society-national, organizational and individual-there are advantages to redefining 20th-century retirement. The notion of establishing a fixed “retirement age,” with the state paying to support retirees, was introduced in Germany in 1889 by Chancellor Otto von Bismarck. The initial German retirement age was 70, later dropping to 65-but this was when life expectancy at birth was perhaps 40 years. Today, German life expectancy is over 80. Franklin Delano Roosevelt brought the same retirement age to the U.S. with Social Security in 1935, when U.S. life expectancy was 61, nearly two decades lower than today’s 79.

Yesterday’s way of thinking about aging must be replaced with something that makes sense for the 21st century. The U.S. can begin by pursuing three reforms.

First, we can change the culture by changing how we measure, and the measure of “unemployment” must better account for older adults. The Bureau of Labor Statistics should update its benchmarks for analyzing the job market. People in their 60s or 70s should be considered eligible for work-but the “unemployment rate” tells us only about conditions for those actively working or seeking work.

How about adding the “employment ratio”-the percentage of men and women 20 years of age and older holding jobs-to the key monthly labor-market indicators? Perhaps also the employment ratio for Americans over 55? That number would tell us that the “work rate” for older Americans has been rising for 20 years, a rare heartening fact about the U.S. workforce these days.

Second, we need policy changes, starting perhaps with a tax credit for firms that invest in training and education for older workers, encouraging what the Japanese are starting to call “silver entrepreneurs.” The Kauffman Foundation estimates that nearly half of all entrepreneurs in the U.S. are over 45. Since they are also among the most successful and productive, this is good policy as well as great business.

Another priority should be worker flexibility across the life-span: making pensions portable and creating incentives for education and training to provide continuing skill enhancement.

Third, corporations must change their approach to hiring, training and retaining talent to capture the abilities of older workers. Some organizations, such as the German car maker BMW, Home Instead Senior Care and the CVS drugstore chain, are already doing this, and it is proving to be good business.

Management of a BMW plant in Bavaria joined with older factory workers to identify how the site could be made “age friendly.” The small, cost-effective changes included softer floors, orthopedic footwear and adjustable workstations. Home Instead Senior Care’s older workers are better able to identify with and understand the needs of its clients. CVS is improving customer service by substantially increasing its over-50 workforce, having heard from customers that they appreciate the advice of older employees.

If human-resources executives took the lead, their influence would spread. Much of today’s “green” movement got its momentum when companies such as Johnson & Johnson, Whole Foods and General Electric got aboard, spreading the environmental message because it made good social and business sense. Though corporations would hire, train and rehire only a fraction of the older population, business leadership would influence society-wide perceptions.

The most common objection to encouraging older Americans to keep working is that they would “steal” the jobs of younger people and create a “gray ceiling.” This is mistaken. Similar arguments were once made about women entering the workforce, but it is now clear that their contributions have been a tremendous economic boon. According to the National Women’s Business Council, female-owned firms have an annual economic impact of $3 trillion and create or maintain more than 23 million jobs.

America’s aging population is a great untapped economic resource. The right policy reforms and business practices could leverage this resource to unleash another century of American economic growth. But first a profound transformation is needed in how we think about work, activity, aging and retirement.

Mr. Eberstadt is a resident scholar at the American Enterprise Institute. Mr. Hodin is executive director of the Global Coalition on Aging and a managing partner at the High Lantern Group.