In a Somerset farmhouse in February, I watched Jet Black, 75, try to force his bulky, broken frame into drumming one more time for The Stranglers on their then looming tour. Suffering from neck, spine, lung and other ailments, even the half hour he hoped to play each night would prove beyond him. But he did play.
The next month, I visited ex-Cream drummer Ginger Baker, 75, at his home outside Canterbury. Ravaged by osteoarthritis and emphysema, lying down to watch cricket on TV was painful enough. But he was preparing to lift drum sticks he confessed sometimes felt like "lead weights" to play again. Last Saturday, John Mayall, the acknowledged "Godfather of British blues", played an 80th birthday gig at Ronnie Scott's, as part of a lengthy world tour. In June, Charles Aznavour will top that with a 90th birthday show at the Royal Albert Hall.
From Leonard Cohen's acclaimed tour last year aged 79 to Chuck Berry, 87, the genuinely elderly are on the road in unprecedented numbers. When even a punk band has to face up to painful old age, why do so many musicians carry on? And what, when their physical capacity is inevitably diminished, do we get from watching them?
"People say I should retire," Black acknowledges. "I have actually, with ill health, reached the situation where I can't do everything I used to do, but I still want to come on and do what I can. And judging by the audience's reactions, they seem to like it." His motivation to press through the pain barrier is clear. "When you get up in the evening and see all those people, all you think about for the next 1½ hours is delivering your best, and if you do, they'll thank you for it. It is the most satisfying thing."
Musicians' addiction to the road and audiences can expose them to embarrassing decline. Sinatra's final years saw him prompted through his most famous songs with a large autocue, in a voice that was a husky shadow of his once impeccable art. The great jazz pianist Oscar Peterson absent-mindedly repeated tunes at his last, sad Albert Hall shows. Last week, BB King, 88, whose "farewell" tour was in 2006 when, though wonderful, he was already diminished by diabetes, apologised to a complaining crowd in St Louis for his erratic performance. Baker and Berry are ghosts of the players they were.
That shouldn't detract from these musicians' achievements at their peak (except perhaps for those mortified fans in attendance). But nor is such infirmity inevitable. Cohen and Aznavour have distilled a lifetime's matchless experience into recent shows, adding to their emotional power. Their tours are a summation, not a sad coda. During Black's brief contributions to the Stranglers' Hammersmith Apollo show in March, his drumming's jazzy swing betrayed pre-rock roots that will be irreplaceable.
Elderly musicians also carry precious treasures of personal and cultural history. David "Honeyboy" Edwards didn't lack for gigs till his death in 2011, aged 96, partly because he was a living link to the blues' most legendary figure, his friend Robert Johnson. A week ago Allen Toussaint, New Orleans' most revered songwriter and arranger, played two nights at Ronnie Scott's. Never primarily a performer anyway, the 75-year-old punctuated his hit "Southern Nights" with a spellbinding evocation of Forties childhood visits to Cajun relatives in a rustic, long-gone Louisiana.
Two years ago, I watched the then 83-year-old Detroit jazz singer Sheila Jordan in a pub back room in south London as she reminisced, between still artful singing, about how Charlie Parker walked into the alley where she was sulking, having been denied entry to see him because she was underage, and played just for her. "Do your thing!" she implored, passing on Parker's encouragement to us.
It's jazz musicians who are already at the advanced age that rock's greats will soon reach, if they're lucky. Watching saxophonist Sonny Rollins at the Barbican in 2012, when he was 80, the truest value of carrying on became clear. Rollins took the stage with a crab-like, sideways shuffle, his spine bent. The long improvisatory flights for which he's famed were shorter now, but still potent. And this man who had permanently proved himself a half-century before goaded himself to do better: "Come on, Sonny, come on!"
Musicians, like actors, loathe leaving the stage. Often, rather than sniggering at assumed senility, we should be grateful. The last act is as much a part of a musical life as its often explosive start. Rollins, fighting his body to find his genius's last reserves, remained great.
Ginger Baker plays Islington Academy, London N1, on 3 May. Charles Aznavour plays the Royal Albert Hall, London SW7, on 1 June