From a Washington Post story by Matt Viser headlined “Biden to mark his 80th birthday, sort of”:

It is a day that has been met with a hint of dread. The nation’s oldest president is hitting a new, and most unwelcome, milestone on Sunday, and no one really wants to celebrate. Even President Biden himself.

“Somebody said my birthday is coming up,” he said recently. “And I said, ‘No, that must be somebody else.’”

When he was asked separately during a radio interview what an 80-year-old Biden would tell a 50-year-old Biden, he immediately responded: “That I’m still 50!”