For centuries, humans have been seeking it--that elusive fountain of youth, a cure for old age. From wrinkle creams and cosmetic surgery, to dietary supplements and hormone therapy, entire industries thrive on our reluctance to grow old. We fear losing our vigor, our social network, our memories, our wealth, yes, even our hair! But suppose up to 75 percent of how long we live and much of how well we age is determined by lifestyle? While scientists disagree on how to prevent the effects of aging, most all agree that you can significantly influence how well you age.