Graying they may be, but these masters of their respective universes each refuse to yield his or her crown. While a lifetime of work without rest used to be the fate of the working classes, retirement now seems passé, with many of the world’s richest deciding that their senescence is best spent in the boardroom. There are signs that, with a rise in life expectancies and the disappearance of pensions, the trend may be catching on among regular working stiffs, too. From the octogenarian chief executive of Viacom to a Beatle who won’t roll over, here are the men and women who keep punching the clock well after making their fortunes.