Is it time for Jumpin' Jack Flash to sit down and put his feet up? News that Mick Jagger is to undergo surgery to replace a heart valve will have come as a surprise to anyone who has seen the Rolling Stones on stage in recent years, where their hyperactive frontman still jerks incessantly about as if his bandmates filled his underpants with itching powder for a joke.
He may be 75 and have a face the texture of a leather suitcase that's been left out on a skip, but he cavorts with more energy than most performers half his age. Keith Richards, Charlie Watts and Ronnie Wood may be firing up the riffs but it is Jagger who personifies the physical vitality of the greatest rock and roll band in the world.
It is a little discussed aspect of the Jagger-Richards axis how they embody contrary aspects of rock's eternal spirit. Richards stands at a perilous angle and plays as if he is about to keel over, his disregard for his physical appearance reflecting rock's devil-may-care cool. He looks like he's ready to blow cigarette smoke in the face of the Grim Reaper.
Jagger jogs from side to side of the stage, twirls on the spot, runs up and down the catwalk, does his little fast foot shuffle, arms flying about, as if youth is a state of mind. He still wiggles his hips, for God's sake, when most of his generation have had theirs replaced.
But it turns out a Rolling Stone can gather moss, or at least furred arteries. The Stones have had to postpone the North American leg of their No Filter tour, which would have seen them play to a million fans over six weeks. Note the operative word there is postpone, not cancel. Jagger's statement said: "I will be working very hard to get back on stage as soon as I can."
Reports from Miami, where the band had gathered to rehearse, suggest that Jagger has told friends he feels great and is already bored of taking it easy. He has been photographed on the beach with his ballerina girlfriend, Melanie Hamrick, 31, and their two-year-old son Deveraux, Jagger's eighth child. Somehow, I really don't think he is ready to slow down.
Plenty of Jagger's contemporaries have announced retirements over the past year, including Neil Diamond (through ill health), Paul Simon and Sir Elton John, although he's dragging it out for at least three years.
Ozzy Osbourne had to postpone his own farewell tour due to ill health. Black Sabbath have already packed it in, and Rush, Kiss, Lynyrd Skynyrd and Blue Oyster Cult have all been taking final, extended bows.
But there is another option, for the star who still wants to perform but finds the rigours of the road increasingly testing on their stamina and tinnitus: the unplugged show. Bruce Springsteen performed a solo acoustic residency in a Broadway theatre for over a year, grossing over US$113 million ($166 m) from 236 shows and making it home to his own bed every night.
But can you really see him sitting on a stool while Richards strums his way through Tumbling Dice, Brown Sugar or Honky Tonk Women? I have watched Jagger sing emotive ballads like Wild Horses without being able to stay still.
In the explosive early years of the Stones, Jagger was the sexiest frontman in rock and roll, with an act pitched somewhere between the swagger of James Brown and flamboyant mincing of a drag act, exuding a femininity that made his masculinity more assured.
Almost every frontman ever since has been influenced by Jagger, either pushing his flamboyance further in the style of Jim Morrison, David Bowie, Freddie Mercury and Steven Tyler or finding tough masculine alternatives, from Springsteen and Bono to Liam Gallagher. As Jagger's youthful beauty waned, he compensated with even more physically energetic movement.
The first time I saw the Stones, in 1982, he was wearing bicycle shorts and racing from one end of the vast stage to the other. I didn't know if I was at a rock gig or a marathon. It has been estimated that he was covering up to 10 miles a show during that tour. When I asked Richards about his songwriting partner's health last year, he didn't mention his heart but did say: "I worry about his joints from all that jogging."
Jagger's father was a physical education teacher, and it has been reported that even in his seventies, Jagger's physical regime involves running eight miles a day, cycling, yoga, kickboxing, meditation and, er, ballet. Jagger was made to move.
As Richards has repeatedly said, the Rolling Stones will go on until one of them keels over. Jagger will return, and when he does, don't expect him to slow down. You can't sing Start Me Up from an easy chair.