Want to know if you’ll make it past 100 years old? Scientists at Boston University have discovered a genetic signature for longevity. The finding is the result of a study of more than 1,000 centenarians, and the researchers plan to offer a free test so people can discover whether they too have the gene. "This is a major breakthrough," says one geneticist. "It shows you that 150 markers [among millions] are all you need to distinguish between people who live to 100 and people who don't."