Barzilai's big plan isn't necessarily less quixotic than those being dreamed up at Silicon Valley biotechs. It's just quixotic in a completely different way. Rather than trying to develop a wildly expensive, highly speculative therapy that will likely only benefit the billionaire-demigod set, Barzilai wants to convince the FDA to put its seal of approval on an antiaging drug for the rest of us: A cheap, generic, demonstrably safe pharmaceutical that has already shown, in a host of preliminary studies, that it may be able to help stave off many of the worst parts of growing old. Not only that, it would also shorten the duration of those awful parts. ("How To Die Young at a Very Old Age" was the title of his 2014 talk at TEDx Gramercy in New York City.)

The drug in question, metformin, costs about five cents a pill. It's a slightly modified version of a compound that was discovered in a plant, Galega officinalis. The plant, also known as French lilac and goat's rue, is hardly the stuff of cutting-edge science. Physicians have been prescribing it as an herbal remedy for centuries. In 1640, the great English herbalist John Parkinson wrote about goat's rue in his life's work, Theatrum Botanicum, recommending it for "the bitings or stings of any venomous creature," "the plague," "measells," "small pocks," and "wormes in children," among other conditions.

According to some sources, goat's rue was also a centuries-old remedy for frequent urination, now known to be a telltale sign of diabetes. Today, metformin, which helps keep blood sugar levels in check without serious side effects, is typically the first-choice treatment for type 2 diabetics, and it's sometimes prescribed for prediabetes as well. Together, the two conditions afflict half of American adults. In 2014 alone, Americans filled 76.9 million prescriptions for metformin, and some of those prescriptions went to Barzilai himself. (He's been taking the drug since he was diagnosed with prediabetes around six years ago.)

A native Israeli, Barzilai speaks English with an accent, never letting grammatical slipups slow him down. He has short, boyish bangs and a slightly rounded face. His thick glasses and natural exuberance give him the look of an actor typecast as an eccentric researcher. He traces his interest in aging to the Sabbath walks he took with his grandfather as a child. Barzilai could never quite reconcile the frailty of the old man with his grandfather's stories of draining swamps in prestate Israel. "I was looking and saying, 'This guy? This old guy could do that?'"

What they discovered was striking: The metformin-takers tended to be healthier in all sorts of ways. They lived longer and had fewer cardiovascular events, and in at least some studies they were less likely to suffer from dementia and Alzheimer's. Most surprising of all, they seemed to get cancer far less frequently--as much as 25 to 40 percent less than diabetics taking two other popular medications. When they did get cancer, they tended to outlive diabetics with cancer who were taking other medications.

As Lewis Cantley, the director of the Cancer Center at Weill Cornell Medicine, once put it, "Metformin may have already saved more people from cancer deaths than any drug in history." Nobel laureate James Watson (of DNA-structure fame), who takes metformin off-label for cancer prevention, once suggested that the drug appeared to be "our only real clue into the business" of fighting the disease.