One morning in early January, David Murdock awoke to an unsettling sensation. At first he didn’t recognize it and then he couldn’t believe it, because for years — decades, really — he maintained what was, in his immodest estimation, perfect health. But now there was this undeniable imperfection, a scratchiness and swollenness familiar only from the distant past. Incredibly, infuriatingly, he had a sore throat. “I never have anything go wrong,” he said later. “Never have a backache. Never have a headache. Never have anything else.” This would make him a lucky man no matter his age. Because he is 87, it makes him an unusually robust specimen, which is what he must be if he is to defy the odds and maybe even the gods and live as long as he intends to. He wants to reach 125, and sees no reason he can’t, provided that he continues eating the way he has for the last quarter century: with a methodical, messianic correctness that he believes can, and will, ward off major disease and minor ailment alike.