At age fifty-one I ran my 17th marathon faster than I had run a decade earlier, and I owe it to a rare sea mollusk from New Zealand! I am no elite athlete. I am just an average Joe who enjoys distance running, but I, like most runners, thought I would get slower with age. I began running marathons at age 37 with a trip to San Francisco and a race raising money for the Leukemia and Lymphoma Society. It was a glorious ...