Until his fiftieth birthday, my dad was like me: overweight, underexercised. But then he found road-biking and turned into Superman. It inspired me—to, you know, just not worry about how fat I was until I turned 50. Fifteen years on, the clock’s ticking, and all the health concerns I once feared for my father are sneaking up on me. So for a week last fall, I took the dive, chasing him and some other olds on an ass-kicking bike tour through France. Could I—or any of us—really just flip the switch? Or was I destined to ride at the back of the pack from here on out?