Donald Trump, 72, left, Joe Biden, 76, and Bernie Sanders, 77. AP File Photos

Age discrimination is a major issue in American society. According to some reports, a majority of people older than 50 will be involuntarily separated from their jobs at least once. But when it comes to our presidential politics, it’s another matter entirely.

President Donald Trump is turning 73 this spring. On the other side of the aisle, the two leading contenders to challenge Trump are Sen. Bernie Sanders, I-Vt., 77, and former Vice President Joe Biden, 76. The two share little in common politically, yet, amazingly, Biden is the top No. 2 choice of Sanders supporters, and those backing Biden return the favor. When infirmities of age are even hinted at, voters across the board seemingly dismiss them. In a recent focus group session of swing voters put together by pollster Engagious, not a single participant said he or she would vote against a candidate because the candidate was too elderly. Other candidates such as South Bend, Indiana, Mayor Pete Buttigieg might say it’s time for a “generational change” in our politics, but it appears few are heeding the message.

How could this be? How can a society that worships youth on the job and in the culture turn into what Malcolm Harris, author of “Kids These Days,” calls a political gerontocracy? Well, you can thank a confluence of factors, ranging from the decadeslong impact of the inordinately large baby-boomer generation, combined with how the particular personalities of a number of older candidates reflect which kind of older candidates we like — and which ones we don’t.

Older Americans remain in a position of political strength in our society. Yes, millennials will overtake boomers as the largest adult age cohort this year, according to the Pew Research Center, but seniors in total (boomers and the remaining members of the silent and greatest generations) are still a larger overall group, as well as a wealthier one. Since older Americans vote at higher rates than their younger peers, they retain outsize strength at the ballot box. “People stay in power for the most part till they are forced out of power,” says Ashton Applewhite, author of “This Chair Rocks: A Manifesto Against Ageism.”

Then there is personality. As I’ve noted in the past, age works particularly well in Sanders’ favor because he plays the long-established role of the elderly truth-teller and moral authority. His positions — down with capitalism, up with increasing Social Security benefits — have been his positions for decades, no matter how unpopular they once might have been. That consistency particularly appeals to younger voters. “Young people are fiercely independent, and I think that’s something Sanders really connects with,” says John Della Volpe, director of polling at the Harvard Kennedy School Institute of Politics. As for Biden, middle-age or young men who are prone to gaffes and invasions of personal space are not endearing or charming. But in old age, Biden became “Uncle Joe Biden,” the cool elderly relative all too many wish turned up at their family gathering.

Our older candidates also use their age to highlight their positions. Trump and Biden hark back to what many of their supporters view as a better past — Biden to the two-term Obama presidency and/or a more bipartisan, less polarized past, and Trump to an earlier era, when men were men, the country was solidly majority white, and prosperity supposedly reigned. No surprise that Trump’s a hit with many senior voters, and he and his team know it: According to Axios, his primary Facebook ad buys target men and women older than 65 with messages about immigration.

It’s also true, however, that all these leading senior candidates are male. We view their female peers very differently. Hillary Clinton was beset by rumors about her health while running for president, even though the obviously overweight Trump — who can’t even recall where his dad was born — still gets a pass from many of the same people. Now it’s Sen. Elizabeth Warren, D-Mass., 69, who’s facing our sexist double standards. Warren has debuted ambitious game-changing plans to offer universal child care and all but wipe out student debt, all while calling out our system for coddling the wealthy at the expense of everyone else. This stuff should be catnip to financially besieged and progressive millennial voters, but Warren is continuing to languish, at least for now. It points to an elemental truth: Only one sex gets to use their age to enhance their status. Women? They need to prove they are not old, again and again and again.