Washington: Joe Biden turned 80 on Sunday, making him the first octogenarian president in U.S. history.

He celebrated his birthday with a brunch hosted by his wife, Jill, a celebration that got an extra lift this weekend with his granddaughter’s wedding at the White House on Saturday.

With Biden already the oldest person to serve as president, the 2024 race for the White House is shaping up to be uncharted territory for the United States. The nearly 250-year old democracy celebrates youth, but millions of Americans – including presidents – are now working well beyond the traditional retirement age of 65.

Ronald Reagan was 77 when he left the White House, but Biden would be 86 by the time a second four-year term ends, should he win it. His leading potential Republican opponent, Donald Trump, would be 82 when he left office if he won in 2024.

As a society, the United States is ageing, and working until later in life. The 65-and-older population is projected to nearly double from 52 million in 2018 to 95 million by 2060. By 2026, more than one in four men over 65 will still be working, the nonprofit Population Reference Bureau projects.

Some Americans have concerns about the advanced age of the two most likely 2024 candidates.

While 71 per cent of Democrats think Biden is “mentally sharp and able to deal with challenges”, 46 per cent say he may not be up to the challenge of running in 2024, according to a Reuters/Ipsos poll taken November 8 and 9. About a quarter of Republicans, 26 per cent, think Trump may not be up to 2024 because of his age.

Political affiliation aside, 68 per cent of people surveyed think Biden may not be up for the challenge two years from now, and 49 per cent say the same about Trump. Some 86 per cent of Americans said they believe the cutoff for serving as president should be age 75 or younger, the poll found.