Activity level is a core but understudied individual difference. Understanding patterns of physical activity over long periods may be key to understanding why some individuals develop healthy lifestyles. The present study transformed qualitative information from the Terman Life Cycle Study to examine patterns of leisure time physical activity across four decades (1936-1972). Activities were converted into metabolic equivalent (MET) ratings, and then activity patterns, individual variation, and child and adult personality predictors of differing trajectories were examined using growth curve modeling. For overall activity, a quadratic model fit best, with decelerating decline as people aged. Males were consistently more active than females. Much individual variation was present, but childhood energy and sociability, and adult extraversion and neuroticism predicted average activity levels and change. Results suggest that physical activity needs to be understood within the context of the individual’s personality and long-term trajectory, not merely current motivations.