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I've been thinking about death lately. Turning 50 can do that to a person.

I exercise regularly, drink water — all of that. But the reality is the life expectancy of a U.S. resident is 76, so most of my sand has run out. And I'm good with it — although that whole Cologuard at-home colon screening thing was weird.

What really got me thinking about death is that when I was born, life expectancy for an American man was around 67. Back then turning a half-century probably felt a little more ominous. But a funny thing happened on my way to a midlife crisis: Its location changed.

Between 1971 and 2020 the number of 50-somethings grew from 53 million to 118 million. By 2060, 1 in 4 Americans will be over 65. None of these numbers are new to us, but the manner in which we talk about aging has been slow to catch up.

For one thing, we continue to define what it means to be old by outdated ideas of youth. U.S. law accepts 18 as adult in part because of the politics surrounding the Vietnam draft. Modern research suggests most human brains take 25 years to fully develop. The 18-49 demographic, the one advertisers salivate over, also became fixed in our culture in the early 1970s, when life expectancy was lower. By 2050, people over 50 will account for 61 cents of every U.S. dollar spent.

That seismic shift in demographics is one of the reasons entitlements such as Social Security are under stress. It's why debate over President Joe Biden's bid for re-election is as focused on his age as it is on his policies. It's why the streets of Paris are filled with protesters — and flames.

According to the New York Times, most of the European Union has already lifted retirement age to over 65 in response to a population that's living longer. France had been at 62. Now it's 64, and President Emmanuel Macron is probably going to lose his job over that shift despite the pragmatism of it all.

The year the United Nations began keeping track of global data, worldwide life expectancy was just 52.5 years. That was in 1960. Today the global average is almost 73.

The breakthroughs in medicine and nutrition that made this possible haven't just thrown off the math behind French pensions and the U.S. health care system. They have shifted the fulcrum that divides youth from old age. They have redefined what it means to be "middle aged" by extending the length of life as a whole.

Healthy people in the developed world are not "old" when they reach 62. A societal expectation to work a few years longer is in many ways a good sign. More and more of us are likely to be hitting a new stride in our career — or even embarking on second or third acts.

The ultraphysical world of sports, with its history of very young "retirement," gives us a preview. Roger Federer retired from tennis last year at 41, and Serena Williams did the same at 40, both with multiple "oldest to" accolades to their names. Tom Brady was 45 as he stunned crowds through the latest NFL season. Last season LeBron James became the oldest player in the NBA ever to average 30 points or more per game. The average age of Olympic athletes in 2021 had risen by two years compared with the 1992 Games.

Two years ago, Phil Mickelson became the oldest major champion at 50, the minimum age to qualify for golf's senior tour. That age requirement is a relic of the tour's humble beginnings from back in 1937, when life expectancy was just 58.

Despite all of the advancements in science and medicine that have clearly extended human life, we still use an age cutoff from a bygone era. It doesn't represent where we are today and more importantly where we are headed.

A survey by ProPublica a few years ago found that 56% of older Americans had either been let go after 50 or been forced to retire. You know the routine — shareholders, budget cuts, yada, yada, yada. Cutting the high end of the payroll has long been a tool to improve the bottom line. But how will that play out in 2060 when 1 in 4 Americans are "old"?

We are in the midst of a fascinating global paradigm shift, parallel to the "great resignation" of recent years in which young people have challenged what work and employment looks like. The evolving expectations for 60-something workers are forcing us to reconsider, even re-legislate, what constitutes an old person.