In 1900, a 30-year-old American could expect to live another 15 years, midway into their 40s. Today, the average American lives to nearly 80. We've effectively doubled human lifespan in a century. But even this dramatic extension of human life feels insufficient when we think about what we're still losing. Einstein and Feynman died at 76 and 69, respectively, and Steve Jobs and Marie Curie both died at 56. My grandfather lost his fight with cancer before getting to see any of his gr...