IN AMERICAN politics, John McCain is living proof that you really are only as old as you feel: if the Arizona senator gets to the White House, he will be the United States' oldest president ever: at 72 two years older than Ronald Reagan when he was elected in 1980.
Yet despite running for office in the world's most youth- obsessed culture, he remains front-runner for today's Florida Republican primary election.
"If you can take the haul of a campaign, you can probably manage the White House," said Nancy Sw
allow, 72, a McCain supporter from Lake Wells, Florida. "I think anybody has got to be off their rocker to run for president, because it's a horrible, gruelling thing to do."
Age can raise its head, as when TV pictures showed president Jimmy Carter collapsing while jogging in 1979 and Republican challenger Bob Dole collapsing in 1996: The images of both men never recovered.
Mr McCain, by contrast, rubs in his vigour by appearing on the campaign platforms alongside his 95-year-old mother, Roberta.
The questions come up again and again because of Mr McCain's age and his three bouts with melanoma, an aggressive and potentially deadly form of skin cancer. They came up on Saturday, even in a newspaper endorsement from the St Louis Post-Dispatch.
But Mr McCain is in ceaseless campaign mode. He answers questions from voters at freewheeling town hall meetings; in between stops, he usually fields questions and banters with journalists on his bus.
"Nobody does this. He's amazing that way," said Senator Joseph Lieberman, who wedged himself into the horseshoe-shaped space at the back of Mr McCain's bus on Saturday for an hour and a half. Mr McCain took questions the entire time.
The 2000 Democratic vice presidential nominee and now an independent who has endorsed Mr McCain, Mr Lieberman said he sometimes couldn't help but doze between events.
Aides try to force Mr McCain to take breaks, but aside from an occasional nap on a plane, Mr McCain almost never rests.
Mr McCain stays active outside politics, too; he hiked the Grand Canyon from rim to rim last summer.
"Age really only becomes an issue when something happens and makes you look old," says Philip Klein, a commentator with The American Spectator. "He's been campaigning very rigorously, and he campaigns with his mother, that pushed the idea of longevity."
Mr McCain is emerging as the most likely man to win in Florida today and take the Republican presidential nomination. Some party faithful even hold the hope that, despite the woes of the Bush administration, Republicans may yet hold on to the White House.
As such, Mr McCain is more Comeback Kid than tired old man. He was all but written off last summer when his poll ratings were in single figures, staff deserted him, money ran out and he was reduced to vacuuming his own office.
His dramatic change in fortune owes much to luck, and a little to a fine political judgment. First, the luck. As chairman of the armed services committee in Congress, Mr McCain appeared to be going nowhere last summer by insisting a surge in troop numbers in Iraq might work.
Then, in the autumn, the White House advocated the surge he had been urging and, at least militarily, the policy began to work.
At the same time, the other candidate running on a national security platform, the former New York mayor Rudy Giuliani ran into trouble. He had been the front-runner with a campaign highlighting his own role in the days after the World Trade Centre attacks, but his polls began to dip when New York firefighters accused him of taking undue credit.
The flaws for the other candidates have also begun to bite.
Mike Huckabee won with support from the Christian Right, but his hardline stance on such things as Aids, has been a turn-off for other Republican voters.
The faith question also causes problems for Mr McCain's main challenger, Mitt Romney: As a Mormon, he draws suspicion from both the Christian Right, who are evangelists, and the nonreligious Republicans who fear his faith is extreme.
Other political players have stayed out of this race, fearing that, after the disasters of the Bush administration, the chances of a Republican being elected to the White House are minimal.
Mr McCain, on the other hand, knows that this is his last chance. He is a veteran in campaigning, having entered the Senate in 1987 and campaigned for the nomination, running against Mr Bush, back in 2000.
And far from wearying him, Mr McCain's age appears to have given him wisdom, most of all in reading the mood of the US.
The electorate is governed by a left-right pendulum so obvious that many pundits simply miss it.
Recent times have seen the rightward swing to Ronald Reagan give way to the leftward swing to Bill Clinton before returning right to George Bush. After nearly eight years of Mr Bush, one of US's most accident-prone presidencies, polls show the country ready to swing left once again, or at least towards a fuzzy liberal centre.
And Mr McCain is well-positioned to take advantage. He is conservative, but parades a series of liberal policies often at odds with the Bush administration.
While supporting the war in Iraq, he nevertheless objects to the torture at Guantanamo Bay, and called for the resignation of Donald Rumsfeld, the former defence secretary, after the horrors of Abu Ghraib.
Despite his tirelessness, Mr McCain seemed weary of yet more questions about his age on Saturday on his campaign bus. He tried to bring the issue around to his judgment.
But how old does he feel?
"I'm continuously surprised that I'm on this earth, and so are people who know my life," Mr McCain said. "I have been the most fortunate person that has ever lived. OK? I am the most fortunate person that you will ever know. I've survived in situations that defy all odds. So I am grateful for every single day, and I know that you can't ever live those days over again.
"And I am grateful for the opportunity to serve. That's why you see my line that I use very often – I'd like to serve a little while longer."
