Latent growth models were applied to longitudinal twin data on markers of aging to investigate genetic and environmental influences on the processes of change with age. The sample included 1957 participants aged 50 to 96 years. Five markers were assessed: forced expiratory volume, mean arterial pressure, grip strength, motor functioning, and well-being. Data were gathered at up to three follow-up occasions at intervals of 3 years. Results indicated monotonic changes with age for all but two variables. Performance on motor functioning and well-being was stable until age 65 or 70, followed by significant decline. Genetic influences on the level of performance were indicated for all five markers of aging. Genetic influences on the slope were found for only three of the variables: motor functioning, mean arterial pressure, and forced expiratory volume. Investigations of the aging process will differ depending on whether the focus is on static performance or change.