“Watch me,” President Biden likes to say when he’s asked — he’s asked a lot, these days — whether he is too old to serve a second term. He is getting his wish.

For the first three years of his administration, in contrast to the last president’s chaotic omnipresence, Mr. Biden kept himself scarce. Now his smallest appearance brings with it a thousand remote diagnoses from armchair gerontologists. A major speech, like his State of the Union address in March, is assessed not for its policy but its fluidity as spoken-word performance. A minor gaffe, like bungling a single sentence at a Philadelphia rally in April, is dissected as possible evidence of decline.

He is facing an image problem that time exacts on everyone. Now the first presidential debate of 2024 is happening months earlier than usual, in part because the Biden campaign wants to overcome a mounting concern that the president, at 81, is not up to four additional years of service. “Old age isn’t a battle; old age is a massacre” — or so Philip Roth’s “Everyman” howled in 2006. Electorally, this year, it might be both.

The president is indeed rather old, older than anyone who has held the office. When he first won his Senate seat in 1972, the current leaders of Britain, France and Italy were not yet born. If Mr. Biden serves a full second term, he will retire to Delaware at 86. Already, after three-and-a-half years in a job that superannuates everyone, he appears a different man from the days of the Covid campaign, his hair thinner, his gait tighter. His age may be nothing but a number. But the perception of his age has become desperately entangled with cultural connotations of elderliness, formed over centuries, handed down to us through religion and literature and art.

His predecessor and rival is also old, and also has trouble speaking clearly. But the same polls that have Mr. Biden trailing the 78-year-old Donald J. Trump, even after the latter’s conviction on 34 felony counts, show too that only one of these men is facing such widespread anxieties about the way of all flesh. The principal roadblock to the incumbent’s re-election, the polls keep telling us, is not policy. Younger Democrats, to his left and right, outpace him down-ballot.

The Greek playwrights, who knew something about picturing democracy, liked to characterize old men with images of desiccation and disintegration. Kings become “dried out,” soldiers are “withered.” The tragedies often feature choruses of elderly citizens (in Aeschylus’s “Agamemnon,” in Sophocles’s “Oedipus the King”), who sing of themselves as shades, dreams, things only half-substantial. When Mr. Biden’s limbs appear inflexible, as they did when he stepped out of his car in Paris this month, or when his eyes seem to drift, like during a Juneteenth shindig on the South Lawn, the president is enveloped in these metaphors of age as a kind of brittleness. The perception of mortality — he has grown thin, he has grown frail — can be more hazardous than any actual impairment. Travel as far as wartime Kyiv and it will stalk you still.

Then again, insofar as a leader embodies or symbolizes the state, his old age (or hers, sometimes) can just as much signify solidity, tradition, conviction. Konrad Adenauer, the first chancellor of West Germany, held the top job until he was 87; his election posters exaggerated his jowls and wrinkles, projecting a restored stability after the nightmare of 1933-45. Germans nicknamed their crafty power broker der Alte, the old guy, and Biden pulled off a similar marriage of advanced age and civil restoration during his 2020 campaign (he was old then, too).

When he shouts down hecklers at the State of the Union, or kibitzes in his aviators with officials half his age, he leans into this archetype of leader as senex, like Homer’s Nestor, Titian’s Farnese pope or Alec Guinness’s Jedi. Wise, perhaps wily. Full of life, if maybe long-winded. But you can be seen as the father of the nation one day and as a doddering senior the next. In the realm of politics you seek fairness in vain.

What is at issue is not capacity but the image of capacity, and one could imagine a brutal contest on those terms. “The younger rises when the old doth fall,” schemes the traitorous Edmund in “King Lear.” But it has to be repeated that there will be no intergenerational challenge at this week’s debate. Mr. Trump apparently dyes his hair while Mr. Biden leaves his white, but he too presents a physical stiffness and verbal distractedness that — were all things equal — should not inspire envy in a rival just three-and-a-half years his senior. (A few days ago, boasting that he had “aced” a cognitive test, Mr. Trump flubbed the name of his doctor, who’s now a member of Congress.)

On your phone the feed perpetually refreshes, but the content remains the same — and in a two-party system with an incumbency bias, this year’s presidential rematch forms only the top layer of a larger collision of old bodies and new media. Senator Mitch McConnell, 82, the outgoing minority leader, froze in place twice at recent pressers.

Senator Dianne Feinstein, who was 90 when she died in office last year, appeared uncertain of her whereabouts when votes were called.

In this gerontocratic malaise our political discourse has grown infirm too, thinning into a pathetic volley of real or confected senior moments. Quite a lot now takes place via selectively edited video clips, captioned for a presorted digital public, each reaffirming that your least favorite leader is as mad or sickly as George III. When Mr. Biden appeared to stare into space at this month’s G7 conference, at least in a 30-second snippet circulated by a Republican campaign team and then many news organizations, he was in fact congratulating paratroopers who’d landed nearby. But the linear news report, the contextualized broadcast, are relics of Mr. Biden’s century. The out-of-context clip is the cheapest, most lethal campaign ad, and no deepfake software is required.

Nothing wrong with wanting your leaders to be vital, but are we only judging a politician’s fitness when we agonize over their shortfalls and missteps? Or might we be exacting a punishment for foreshadowing, in their aging national body, the fate that awaits us all? In “Ran,” Akira Kurosawa’s grand 1985 epic of samurai senescence, a Lear-like warlord believes he can bend the realm to his will one final time — but finds, too late, that politics is moving faster than he can keep up with. The succession plan goes wrong. An almighty battle is unleashed. The warlord wanders through the high grass, his white hair streaming, and discovers he is now just another old man. “I’m lost,” the old ruler says. “Such is the human condition,” says his fool.

Video production by Ang Li and Caroline Kim.