Matt Rourke / AP

When Joe Biden climbed to the stage in California to celebrate his Super Tuesday comeback in the Democratic primary, three things happened in a matter of minutes. He basked in the thunderous applause from the crowd. He mistook his wife for his sister. And he delivered the sort of confusing, intermittently slurry, and occasionally indecipherable oration that has defined so many of his recent public appearances.

One might expect a typical opponent to seize on these verbal slips by questioning whether Biden, who is 77, is too old to hack it. But his rival Bernie Sanders, who has already suffered a heart attack during this campaign, is a year older. In January 2021, the three people most likely to be the next president—Biden, Sanders, and the incumbent, Donald Trump—would each be the oldest president to ever give an inaugural address in American history.

We have now before us three candidates divided by ideology, but united in dotage. All three white men were born in the 1940s, before the invention of Velcro and the independence of India and Israel. Amazingly, each is currently older than any of the past three U.S. presidents. If, through some constitutional glitch, Bill Clinton, George W. Bush, or Barack Obama jumped into the 2020 race at this very moment, each would suddenly become the youngest man in the contest.

How did this happen?

One possibility is that it’s mere randomness. It’s only one election that’s been roiled by Trump, you might think, and younger blood is waiting in the wings. But old age runs deep in modern presidential politics. Elizabeth Warren would also be the oldest president-elect in American history. The losers of the past two presidential elections, Mitt Romney and Hillary Clinton, were born months apart in 1947.

The mystery of America’s old presidential candidates is really two separate questions—one of demand, and one of supply. First, are there reasons today’s voters might prefer older candidates to younger ones? And second, why is the pipeline of viable presidential candidates so advanced in years?

The most obvious reason America’s presidential candidates are so old might be that Americans are getting older. Voters over 65 routinely go to the polls more often than young voters do, and political-science research has found that voters typically prefer candidates “who are closest to themselves in age.” This sounds like a universal formula: Older countries produce older politicians.

But since the 1980s, almost every European country has gotten older, while the typical European Union leader has actually gotten younger. In the United Kingdom, although people over 55 outvote people under 30 by one of the widest margins in the world, the current prime minister, Boris Johnson, is “only” 55. Biden, Sanders, and Trump are all older right now than the U.K.’s five previous prime ministers, going back to Tony Blair.

So the preference for very old candidates seems to be weirdly, specifically American. What’s that about?

Maybe it’s about decades of youth disengagement from politics. According to The Economist, older Americans have outvoted younger Americans by a wider margin than in the typical OECD country. This is particularly true at the local level. As Timothy Noah writes in Politico, studies have found that the median voter age in America’s municipal elections is 57—“nearly a generation older than the median age of eligible voters.”

Or maybe it’s about the American electorate’s preference for “experienced novices.” Since 1996, every new president has had less national political experience than the previous commander in chief had when he was elected. Bill Clinton was a fresher face than George H. W. Bush, but had more gubernatorial experience than George W. Bush, who in turn was a governor for longer than Barack Obama was a senator. And then came Trump, who had no political experience at all. If you extrapolate this trend, it might sound like America’s next breakthrough presidential candidate will be some 35-year-old YouTube influencer who just recently learned about the filibuster.

But audiences tend to gravitate toward extreme novelty when it’s paired with deep familiarity. Most people want to feel mildly surprised and simultaneously comforted by their media, whether film, television, or music. The perfect “familiar surprise” in politics might be a character quite like Trump: a well-known celebrity who also represents a shock to the political system. If the future of American politics is experienced novices, the scale may be subtly tipped toward comforting paternal figures who aren’t steeped in the poison of contemporary politics, either because they’ve been out of the game (like Biden) or because they’ve consistently rejected its rules (like Sanders).

American leadership is old folks, all the way down.

The U.S. government is a creaky machine whose most crucial cogs could be generously described as “vintage.” The average age in Congress is near an all-time high. The House speaker, House majority leader, House majority whip, and Senate majority leader are all over 75.

To be clear, this phenomenon is bigger than politics. Across business, science, and finance, power is concentrated among the elderly. In the past 40 years, the average age of Nobel Prize laureates has increased in almost every discipline, including physics, chemistry, medicine, and literature. Among S&P 500 companies, the average age of incoming CEOs has increased by 14 years in the past 14 years. Americans 55 and older account for less than one-third of the population, but they own two-thirds of the nation’s wealth—the highest level of wealth concentration on record.

The prevalence of old power is undoubtedly related to the prevalence of old age. Higher-income Americans are living longer than ever and working longer, too. Leading the country is tiring work (at least in theory) but it’s not taxing in the way that factory work or construction is. As the economy shifts to white-collar labor, septuagenarians are staying at work. The share of Americans over 75 who are attached to the labor force has increased by 85 percent in the past 20 years.

The expense of presidential politics also disproportionately benefits the old.

Older politicians have had longer to build up donor networks, and older rich people may be more likely to take the risk of self-funding. If Jeff Bezos had quit Amazon to run for president this year, he would have given up years of peak earning and peak productivity in the private sector. Trump and Bloomberg, meanwhile, are wealthy grandfathers whose most significant private-sector achievements are behind them. They can afford to run for president on a lark, both in a literal sense (they can obviously afford to) and in an existential sense: What else is Bloomberg going to do in his 80s, other than spend his money on political causes, including the cause of himself?

To quarrel with a thousand Hallmark copywriters: Age is not just a number. And rule by the old is not harmless.

First, gerontocracy is a cousin to plutocracy. Power concentrated in the hands of old people who are also rich will predictably lead to policies that benefit the old and the rich, at the expense of the less privileged. The federal government already guarantees universal health insurance and a universal basic income to seniors, even as Republicans cry socialism when young people request versions of the same policies. It’s unlikely that young people will notch many policy wins in a government whose median age is over 70.

Second, old governance can be bad governance. At the end of the Cold War, a common criticism of the U.S.S.R. was that the country was crumbling in part because the Soviet politburo was too old and out of touch to keep up with a changing world. Research indicates that cognitive deterioration typically accelerates in one’s 70s. Without encouraging voters or employers to be ageist, it seems risky to leave the most important issues of life, death, and welfare in the hands of a group of septuagenarians who are in the crosshairs of biologically predictable cognitive decline.

Finally, the most important challenge before the U.S. and the world—climate change—is profoundly intergenerational. Solving it requires a farsighted approach to diplomacy, invention, and technological deployment that a creaky old country will simply never master. This crisis urgently requires the input and ideas of the generations that will be most affected by it. If government of the elderly, by the elderly, and for the elderly will not perish from the Earth, the rest of us might suffer instead.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.