Aren’t old people delightful? So feisty! Such spunk! When they’re not threatening your five-year-old with an iron bar, they might be off practising kung fu on would-be teen muggers (and quite rightly – punks) or dispensing advice to lad mag readers. This much is clear: retirement just isn’t what it used to be. Witness Buster Martin, the 101-year-old with an invincibility complex. And no wonder. After first gaining notoriety for refusing to take a......