Rarely is the president of the United States, nestled in his box, the center of attention at the Kennedy Center Honors, the annual awards ceremony that brings a carousel of celebrities, musicians and actors to the stage to pay tribute to lifetime achievements in the arts.

But such was the case on Sunday night, when Robert De Niro, celebrating Billy Crystal’s career, marveled at all the honoree had packed into his career.

“You’re only 75,” Mr. De Niro said. “That means you’re just about six years away from being the perfect age to be president.”

As President Biden grinned, waved and ruefully shook his finger at Mr. De Niro from the presidential box, members of the audience leaped to their feet with applause — some to gawk at Mr. Biden’s reaction from the front row of the balcony.