It is astonishing, isn't it? I'm reading Sirens of Titan right now and luck is such a big theme in it. You can always increase your odds by healthy living, but nothing is guaranteed. It really comes down to dumb luck.
Let's not forget Ozzy's immense wealth that allowed him the best medical care and health/fitness programs in his later years. He stopped living "hard" by the 2000s, at least by his 1980s standards.