We use panel data from the National Longitudinal Survey of Youth (NLSY) to examine how body weight changes with age for a cohort moving through early adulthood, to investigate how the age-obesity gradient differs with socioeconomic status (SES) and to study channels for these SES disparities. Our results show first that weight increases with age and is inversely related to SES during childhood. Second, the obesity gradient widens over the lifecycle, consistent with research on other health outcomes. Third, a substantial portion of the "effect" of early life conditions operates through race/ethnicity and the translation of advantaged family backgrounds during childhood into higher levels of subsequent education. By contrast, little of the SES gap appears to propagate through household composition, family income or health behaviors. Fourth, adult SES has independent effects after controlling for childhood status.