There are numerous risk/protective factors for developing mental disorders in older people. This study examined the contribution of lifestyle (physical activity, sedentary behavior, smoking habits, and alcohol consumption) and psychosocial resources (optimism, resilience, social support, and frequency of social contacts) to older people’s mental health. We conducted the study on a community-dwelling sample of 780 persons (58% women) aged 65–98 from different geographical regions of the Republic of Croatia. We administered the questionnaires, including relevant instruments, individually. We found no differences in mental health regarding smoking habits. On the other hand, individuals who consumed alcohol had better mental health than those who did not drink alcohol, primarily because of gender differences in alcohol consumption and mental health. Physical activity was significantly positively associated with mental health. The regression analysis results showed that psychological resources (optimism and resilience) were significantly better predictors of mental health than lifestyle factors and social resources. The study’s results emphasize the importance of psychological resources as protective factors for older people’s mental health.