Schubert died even younger, at 31. Why should his late music have such an air of spiritual wisdom? He contracted syphilis when he was 25; his music was haunted by death thereafter, or so the theory goes. Yet Schubert's premature death was rather sudden: he contracted a serious illness, possibly typhoid fever, from eating fish. From what turned out to be his deathbed, he wrote to his brother asking for a James Fenimore Cooper novel. He did not expect to die; he could have lived on with syphilis for years. Some of the visionary terror in his "late" music could be attributed to the awareness that he was facing a terrible, incurable illness — but he had written his spine-chilling song Erlkönig when he was only 16. To him, as to Mozart, death was part of life from the start and awareness of it figured strongly in his outlook.

Schumann's case was rather different. He spent his last two years in a mental hospital; unlike Schubert, syphilis was indeed killing him. His "late" music has often been considered "difficult". But that view, uncomfortably, can be traced back to his wife, Clara, who suppressed and even destroyed some of his late works, terrified that they might give the impression that he was mentally ill. Yet what if Schumann's late works weren't the product of a failing mind, but a push into the future? What's certain is that some — the Gesänge der Frühe and the slow movement of the Violin Concerto — are incredibly beautiful. With Schumann, beware of received opinion.

Beyond Mahler, later composers were frequently forced to face danger, exile and the risk of premature death. Yet as the 20th century progressed, the concept of "late works" carried less power. Some commentators think that Shostakovich's late works are haunted by the fear of death; others suggest that an underlying terror had always characterised his style. Bartók's late Viola Concerto seems bathed in the autumnal glow of the hills around Buda, remembered from New York. But given that he had leukaemia and was living in straitened circumstances after fleeing wartime Hungary, his last work, the Third Piano Concerto, feels remarkably sunny. 

Today the endgame syndrome has dissipated, possibly because we're shielded from the reality of death. In the West, relatively few of us now die young; inevitable mortality is pushed aside as if it simply shouldn't happen. Beyond plastic evocations in films and impersonal news reports, death is a cultural taboo. No such taboo figured for Mozart or Mahler.

The Ninth Symphony may end quietly, but Mahler is not going "gentle into that good night": it takes tremendous control to create such a work. Perhaps the recognition that his time might be limited induced him to muster, urgently, the very best of his abilities. Leonard Bernstein put it perfectly, writing: "It is terrifying, and paralyzing, as the strands of sound disintegrate [...] in ceasing, we lose it all. But in letting go, we have gained everything."

I'd add only that today the world's three most revered living composers are Arvo Pärt, Henri Dutilleux and Elliott Carter. They are respectively 75, 95 and 102. They are still composing.