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The so-called greatest generation that reached adulthood in time to serve in World War II produced U.S. presidents from John F. Kennedy to Ronald Reagan and George H.W. Bush. The mantle then passed to postwar baby boomers: Bill Clinton, George W. Bush, and Barack Obama.

Maybe – belatedly – it is the silent generation, sandwiched in between those two cohorts, that now may have its turn.

Both of the final major candidates in the Democratic primary, Joe Biden and Bernie Sanders, fall into this generational no man’s land. They were born during World War II. President Donald Trump, born just after the war, is officially a boomer.

In recent years the United States elected its first African American president and nearly elected its first woman, Hillary Clinton (although she took the popular vote). During this latest Democratic primary, with its unprecedented diversity of candidates, voters whittled down the choice to Mr. Biden and Mr. Sanders in the end. By the current standards of diversity, they are widely perceived as simply old white men.

Indeed, all three candidates are older than the three most recently retired presidents: Messrs. Clinton, Bush, and Obama. And whoever wins the election in November, he will be the oldest person to hold the office.

Yet that should not be the focus. Life expectancy charts show Americans in their mid-to-late 70s can, on average, live another decade or more – plenty of time to serve a term as president. The real question is not about age but competence. Does a candidate have the energy and acumen to do the job regardless of age?

Those who study aging say common beliefs about older people have radically changed. Yet we are still in unexplored territory. Having the oldest president will be both a sign of the times and a signal for a more expansive view of aging.

“We do know plenty of people are doing all kinds of other stressful work into their 80s,” Louise Aronson, a geriatrician at the University of California, San Francisco, told The New Yorker, “and also that being president should be a team sport. It’s about the ability to use good judgment to surround yourself with really good, competent people and manage them.”

Concern about the age of the current candidates will put a magnifying glass on their choice of running mates, notably their youth and qualifications. Mr. Biden has openly talked about serving only one term. Mr. Trump, if he wins, cannot run again.

With so many seniors breaking mental and physical barriers these days, the U.S. is ripe for a test of its presumed limitations about the age of a president. Even as this year’s candidates are showing youthful vigor, voters can show some rigor in updating views about aging.