One possible explanation is Mr. Biden himself. Older voters appear to have a favorable view of him, and it’s not hard to imagine why they might see him in a more favorable light than Barack Obama, Hillary Clinton or even John Kerry.

He is the first white male Democratic nominee since 2004, and he is probably the first one since 2000 or perhaps earlier who won’t easily be dismissed as a liberal. He is not campaigning on the kind of culture war issues, like immigration, racial justice or gay marriage, that have tended to work to conservatives’ advantage with this group for decades. In other words, older voters may like him for many of the same reasons he disappoints young progressives.

Another possible explanation is Mr. Trump — and perhaps especially his coronavirus response. Older people are relatively vulnerable to the coronavirus and relatively insulated from the effects of an economic shutdown. The president’s drive to reopen the economy, and questions about his slow response, may resonate very differently for a retiree who backed Mr. Trump than for a young parent struggling to support children. A recent Morning Consult poll found that Mr. Trump’s approval rating on the coronavirus response was lower among seniors than among any other group.