(WASHINGTON) — President Joe Biden is celebrating his 81st birthday on Monday, as questions about age continue to dominate the 2024 election.

Biden is the oldest commander in chief in U.S. history. If reelected, he will be 82 at the start of his second term and 86 when it ends.

Former President Donald Trump, the Republican front-runner, isn’t far behind at 77 years old. But Biden has so far faced more scrutiny over his age than Trump, though both have experienced noticeable blunders on the campaign trail.

Biden’s common refrain to those who press him on his age has been to “watch me.” The administration defends his stamina and underscores his record when questioned about his ability to do the job, with his stiff gait and verbal gaffes regularly seized on by critics and Republicans.

“I get the question on age. Certainly, we all do,” White House press secretary Karine Jean-Pierre said in September. “But what we’re going to continue to talk about is the record that this president has had. It’s been a historic record.”

But poll after poll shows the issue is still top of mind for voters.

Three-quarters of Americans (74%) said Biden was too old to run for another term in a survey conducted by ABC News and the Washington Post in September. That number represented a 6% increase since May, a month after Biden launched his second White House bid.

Half of Americans (50%) thought the same of Trump, according to the poll.

A CNN survey out of New Hampshire — which will hold the first presidential primary in January — found 56% of likely Democratic primary voters said age was their biggest concern regarding Biden. The poll, conducted by the University of New Hampshire, was released last week.

Biden frequently jokes about his age on the campaign trail.

“I know I’m 198 years old,” he quipped back in June while giving remarks on the one-year mark of the U.S. Supreme Court overruling Roe v. Wade.

“I’ve never been more optimistic about our country’s future in the 800 years I’ve served,” he said at a campaign reception in New York in September.

Questions about age and politics are not limited to Biden. This year, alarming episodes involving longtime Republican Senate leader Mitch McConnell and powerhouse Democrat Dianne Feinstein, who died in September, made headlines and stoked fierce debate about how old is too old to serve in public office.

S. Jay Olshansky, a professor of public health at the University of Illinois at Chicago, previously told ABC News such a question is “unanswerable.”

Last year, Biden marked his milestone 80th birthday with a subdued brunch at the White House with his family. At the time, Biden was mulling whether to run again as other veteran Democrats like former House Speaker Nancy Pelosi were announcing they were stepping down from their leadership roles to usher in a new generation.

Biden made a passing reference to his birthday last week as he met with Chinese President Xi Jinping at the Asia-Pacific Economic Cooperation summit in San Francisco.

According to a senior administration official, Biden wished President Xi’s wife a happy birthday as the two share the same birthday. Xi thanked Biden for reminding him, stating he’d been “working so hard that he had forgotten his wife’s birthday” was approaching.

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