The purpose of this longitudinal study was to investigate age (60, 80, and 100 years), gender, and ethnic (Blacks and Whites) differences in mental health in community-dwelling older adults from the Georgia Centenarian Study and to assess mediating and moderating effects (i.e., social support, life events, and subjective health) on the relationship between demographic variables and mental health. Three mental health areas were assessed: life satisfaction, morale, and depression. We examined 321 participants at Time 1 (T1) and 201 participants at Time 2 (T2). The results suggest that centenarians had lower levels of life satisfaction at T1, morale (T1 and T2), and higher levels of depression (T1 and T2) compared to sexagenarians and octogenarians. Gender differences were only found for depression at T1. Women reported higher levels of depressive symptoms compared to men. There were no mean differences between men and women on the other mental health dimensions. No ethnic differences were obtained for mental health. Social support and perceived health mediated the relationship between demographic variables and mental health. Finally, when assessing moderating effects, social support moderated the relationship between age (60 & 80 years) and life satisfaction, indicating that older adults had higher life satisfaction even when receiving low social support. Health positively moderated the relationship between ethnicity and depression, suggesting that Blacks (but not Whites) reported high depressive symptoms even when reporting good health.