Welcome to the revolution. For as long as anyone can remember, we've associated midlife with unwelcome life changes and stagnation. It's been a harbinger of future decline and potential disability, a time when people begin to worry about being "over the hill." The truth is, people between the ages of about 45 and 65 are at the top of the hill. Since 1900, we have increased life expectancy from 47 to nearly 80 years, and many of us will live even longer...