In 1881, the conservative German Chancellor Otto von Bismarck, plagued by a rise in socialist ideology, proposed a national retirement benefit to appease the leftist masses.

He set the retirement age at 70. Average life expectancy at the time? About 40 years. Von Bismarck resigned shortly after the policy passed, but his legacy remained, and Germany's retirement benefit (which was lowered to 65 in 1916) became the model for many other nations.

When President Roosevelt established the Social Security Act of 1935, 65 was similarly chosen as the national retirement age, despite the fact that less than 60 percent of American adults lived that long.

Which is all to say, the national retirement age in the U.S. and elsewhere has origins in a bit of political smoke and mirrors; it began as a symbolic offering, accessible only to the lucky citizens who managed to survive well into old age.

Today though, many more people live long enough to have access to a national retirement fund, often for years if not decades. Average life expectancy in the United States is 76, and in many European countries it's even higher.

The U.S. national retirement age -- when you can start claiming full Social Security benefits -- has crept up much more gradually, to 67 for people born after 1960.

In response, several countries -- most notoriously France, where the retirement age is 62 and life expectancy is 82 -- are debating raising the retirement age to try to offset the economic pressures of an aging population and the concern that national retirement benefits won't be able to keep up for much longer.

From an economic standpoint, a later retirement age perhaps benefits everyone's bottom line. But putting finances aside, what are the mental and physical implications of raising a national retirement age? We asked experts to weigh in.

One way to answer this question is to look at changes not in life span but in health-span -- the number of years people are healthy and disability-free. Think of it as your work-span.

Gal Wettstein, a senior research economist at the Center for Retirement Research at Boston College, looked at age and potential for employment in a study about people's working life expectancy.

He found that Americans who are healthy at age 50 can expect to have roughly 23 more years free of disability, plus about eight years living with disability. That would suggest people's maximum working life expectancy, on average, is age 73.

"There's no doubt that life expectancy is longer, and also the ability to work has expanded," Dr. Wettstein said. "Part of that is medical changes, and part of that is the nature of work has changed."

In 2020, roughly 45 percent of the American labor force worked in a knowledge-based field, such as management, business and finance, education and health care. In 1935, these types of professions accounted for just 6 percent of the workforce.

Dr. Pinchas Cohen, dean of the Leonard Davis School of Gerontology at the University of Southern California, agreed that, from a health standpoint for people in these fields, a retirement age under 65 "makes no sense." "Even 65 is a 20th century number," he said.