For thousands of years, magicians, alchemists, even a few fringe medical practitioners have fueled an unbounded optimism that we can blunt the ravages of time, stay younger for longer, maybe even defeat death itself. Their pitches have usually hinged on some drug, food or device — everything from electricity to yogurt to surgically installing the gonads of animals into our own bodies — that will slow or reverse the aging process. Every decade or so, “anti-aging” promoters grasp onto news coming out of research labs and trumpet those developments as the answer we have all been awaiting.