"Caroline Paul has always filled her life with adventure: From mountain biking in the Bolivian Andes to pitching a tent, mid-blizzard, on Denali, she has never been a stranger to the exhilaration the outdoors can hold. Yet through it all, she has long wondered, Why aren't women, like men, encouraged to keep adventuring into old age? Tough broad is her quest to understand not just how to live a dynamic life in a changing body, but why we must. She...