The authors hypothesized that 1) physical growth, as a marker of the early development of muscle fibers, and 2) advanced childhood motor and cognitive abilities, as markers of central nervous system development, would be positively related to midlife standing balance and chair rising, independently of later life experiences. They tested these hypotheses in a representative British sample of 1,374 men and 1,410 women aged 53 years in 1999 with prospective childhood measures of heights and weights, age at first standing and walking, cognitive ability, and motor coordination. Weight gain before age 7 years was positively related to adult performance in men but not women, independently of later body size, social class, physical activity, and health status. Attainment of motor milestones at the modal age and higher scores on tests of cognitive ability and motor coordination were associated with better performance, independently of other factors. This study is the first to show that childhood growth and development affect midlife performance; prevention of disability and frailty in later life may need to start early.