This study examined whether the emotional benefits of dispositional optimism for managing stressful encounters decrease across older adulthood. Such an effect might emerge because age‐related declines in opportunities for overcoming stressors could reduce the effectiveness of optimism. This hypothesis was tested in a 6‐year longitudinal study of 171 community‐dwelling older adults (age range = 64–90 years). Hierarchical linear models showed that dispositional optimism protected relatively young participants from exhibiting elevations in depressive symptoms over time, but that these benefits became increasingly reduced among their older counterparts. Moreover, the findings showed that an age‐related association between optimism and depressive symptoms was observed particularly during periods of enhanced, as compared to reduced, stress. These results suggest that dispositional optimism protects emotional well‐being during the early phases of older adulthood, but that its effects are reduced in advanced old age.