People in their 80s lead countries, create majestic art and perform feats of endurance. One entered the record books for scaling Mount Everest.
It's soon time for Joe Biden, 80 last weekend, to decide whether he has one more mountain to climb -- the one to a second term as president.
Questions swirl now, in his own party as well as broadly in the United States, about whether he's got what it takes to go for the summit again.
The oldest sitting president in history, Biden hits his milestone birthday on Sunday at a personal crossroads as he and his family face a decision in the coming months on whether he should announce for re-election. He'd be 86 at the end of a potential second term.
Biden aides and allies all say he intends to run -- and his team has begun quiet preparations for a campaign -- but it has often been the president himself who has sounded the most equivocal.
"My intention is that I run again," he said at a news conference this month.
"But I'm a great respecter of fate. We're going to have discussions about it," he said.
Aides expect those conversations to pick up in earnest over Thanksgiving and Christmas, with a decision not until well after New Year's.
To observe Biden at work is to see a leader tap a storehouse of knowledge built up over a half century in public office as he draws on deep personal relationships at home and abroad, his mastery of policy and his familiarity with how Washington works or doesn't. In short, the wisdom of the aged.
"There is something to be said for experience," said Dartmouth College historian Matt Delmont as he noted the dozens of global leaders in their 80s.
But to observe Biden is also to see him walk now often with a halting gait, in contrast to his trotting on stage on election night in 2020.
It is to see him take a pass on a formal dinner with other world leaders without a real explanation, as happened on his trip abroad this past week, when he twice spoke of visiting Colombia when he meant Cambodia. Some supporters wince when he speaks, hoping he gets through his remarks OK.
Biden's verbal flubs have been the stuff of legend throughout his five-decade political career.
In the distorted mirrors of social media commentary, every slip is magnified into supposed proof of senility. A moment of silent reflection by Biden in a meeting is presented as the president nodding off. All of that went into Donald Trump's quiver of falsehoods when he announced on Tuesday that he will seek the presidency again.
Some allies see Biden's blunders as an increasing vulnerability in the eyes of voters as he's grown older.
In an AP VoteCast survey of the electorate this month, fully 58 per cent of voters said he does not have the mental capability to serve effectively as president. That was a grim picture of his standing now, not just looking ahead to another potential term. Only 34 per cent said he's a strong leader.
Those findings come alongside notably low approval ratings in league with Trump's at this point of their presidencies.
Biden is already in the club of high achievers for people his age. Unlike 92 per cent of people 75 and over in the US, he still has a job, not to mention a mightily demanding one.
And he's been on a roll. The November elections produced the best result for a Democratic president's party in midterms in decades -- despite the poison pill of high inflation -- as Democrats kept control of the Senate, narrowly lost the House in defiance of expectations of a rout, and won several competitive governors' races in key states.
The president also sealed a string of consequential legislative victories in recent months, on climate, infrastructure, health care expansion, military aid to Ukraine and more.
Biden says he begins most days with an 8am workout, when he is usually joined by his personal trainer and physical therapist, Drew Contreras, if he doesn't ride his Peloton bike.
"If I let it go for a week, I feel it," he told the Smartles" podcast recently.
"I used to be able to go for a week and nothing would change."
White House aides say Biden reads his briefing book deep into the night, holds intensive evening meetings with advisers and has never baulked at their scheduling requests that may have him out late, though rarely up early.
Yet his aides are deeply protective of the president, especially with his public schedule, which is lighter than those of Barack Obama and George W Bush, both far younger in office. They've shielded him from formal interviews and, until recently, press conferences.
To his doubters, he says: "Watch me."
Biden has been diagnosed with several very common age-related health conditions, none causing him serious problems.
In his November 2021 summary of Biden's health after the president's first full physical in office, Dr. Kevin O'Connor noted Biden's gait had become somewhat stiffer, something doctors watch for in older patients as it could signal a fall risk.
But after testing, the doctor concluded it's mostly due to ongoing "wear and tear" arthritis of the spine, as well as compensation for a broken foot sustained a year earlier and the development of "mild peripheral neuropathy" or subtle damage to some sensory nerves in the feet.
Experts say age is not destiny; what matters is good health, fitness and functioning. Japanese climber Yuichiro Miura had enough of those attributes to make it to the top of Mount Everest in 2013 at age 80, setting a record that an 85-year-old Nepali man died trying to break in 2017.
Growing old is inexorable -- at whatever pace, it comes.
Supreme Court justices, shielded from the electorate and bosses, can grow as old in the job as they want and as fate allows -- and they tend to stick around. Justice John Paul Stevens retired in 2010 at 90, attributing his decision to a small stroke while reading his Citizens United dissent from the bench.
Ruth Bader Ginsberg, a hugely consequential 80-something, fell three years short of her goal to be as old as Stevens on the bench. She died in September 2020.
In democracies, where voters are the boss, and in autocracies, where they're not, plenty of people in power soldier on in their advanced years, even if few are up there like former Malaysian prime minister Mahathir Mohamad, who became the world's oldest leader at 92 and is running to get the office back, at 97.
Much of the leadership in the US Congress is over 70, especially Democrats, and so were Biden's main rivals in the 2020 Democratic primaries and Trump.
Attribute that, in part, to increasing longevity.
When a perception does take hold in the public, any slip-up can feed it, whether it is relevant or not.
When Biden tumbled on his bicycle in Delaware in June, his foot or feet caught in the pedals' cages, the mishap fed the perception of a president not at the top of his game physically.
Ageism pops up in campaigns even when opposing candidates are both old themselves. Witness Trump's references to "Sleepy Joe" in 2020 and Biden's characterisation of Trump as "mentally deranged".
But it was particularly pronounced in the 2008 presidential contest between Obama, 47 in that autumn's campaign, and Senator John McCain, then 72.
But the sharpest cracks about age came from McCain himself.
"Good evening, my fellow Americans," he said on Saturday Night Live.
"I ask you, what should we be looking for in our next president? Certainly someone who is very, very, very old."