For people working in knowledge-based jobs, a retirement age in the 70s is reasonable from a cognitive perspective, too, said Lisa Renzi-Hammond, director of the Institute of Gerontology at the University of Georgia.
"Our cognitive faculties we're able to maintain, usually, pretty well into our 70s," she said. "If retirement age is set based on the capabilities or competence of employees, there's absolutely no reason to have a retirement age in the 60s."
Parts of the brain -- most notably the prefrontal cortex, which is critical for executive functioning, attention and working memory -- do start to lose volume as early as around age 45, but other areas are able to compensate, Dr. Renzi-Hammond said.
And other aspects of cognition, such as crystallized intelligence (accumulated knowledge that can be applied to new situations) and social cognition (behaving appropriately in interpersonal interactions), continue to improve for decades.
Many of these cognitive processes are maintained and strengthened by staying in the work force. Consequently, some people decline mentally and physically when they stop working.
One study even found that delaying retirement was associated with a decreased risk of death, regardless of health before retirement. Experts speculate that the losses of job-related physical activity and social interactions that come with leaving work are largely to blame for post-retirement declines.
National health and disability averages don't tell the full story, though. While some people stay sharp and continue to work into their 80s, other jobs are more physically demanding and take a toll on people's health.
"There are people who do manual labor where at age 65, they really cannot continue to do this very challenging work," Dr. Cohen said. "Their need to retire needs to be respected."
For these types of work, retirement can actually improve health outcomes, Dr. Renzi-Hammond said. "If you're leaving a job that is physically bad for you, where you are getting terrible sleep and you're constantly stressed out, then retirement is great for your health."
Life span and health-span are also not consistent across race and gender, both because of the type of work certain demographics are more likely to take part in, and the toll chronic stress from discrimination takes on the body.
In his research, Dr. Wettstein found that, at age 50, Black men have a working life expectancy of approximately 17 years, while white women could continue working for 24 years. "There is an equity concern there, both on the life expectancy side, and also on the working-life expectancy side," Dr. Wettstein said.
"We know that Black Americans, particularly, develop illness at earlier ages, live with more disabilities, die younger," said Dr. Lisa Cooper, director of the Johns Hopkins Center for Health Equity. "So not allowing them to retire until they're older means they're just not going to benefit from Social Security as much."
This is also true for people from lower income brackets and those who work in physically intense jobs, she added. As a result, Dr. Cooper said, "Raising the retirement age needs to be done with all of these issues in mind, because it's not going to affect everyone the same."
The initial intent for Social Security when it was established in 1935 was simply to sustain people once they could no longer physically work. But another way to think of federally funded retirement is that it should reward people with a few years of leisure.
"One of the areas that we don't talk enough about is: What do people deserve?" Dr. Cohen said. "Is a few wonderful years when you're still healthy -- that you can do things and travel and so on -- is that a national goal?" In France, and likely elsewhere too, many would say yes.