Little is known about how optimism differs by age and changes over time, particularly among older adults. Even less is known about how changes in optimism are related to changes in physical health. We examined age differences and longitudinal changes in optimism in 9,790 older adults over a 4-year period. We found an inverted U-shaped pattern between optimism and age both cross-sectionally and longitudinally, such that optimism generally increased in older adults before decreasing. Increases in optimism over a 4-year period were associated with improvements in self-rated health and fewer chronic illnesses over the same time frame. The findings from the current study are consistent with changes in emotion regulation strategies employed by older adults and age-related changes in well-being.