Mild depression and anxiety were investigated in relation to measures of within-person (WP) variability and mean reaction time from psychomotor, executive function, visual search, and word recognition tasks in a continuous age range (18–85 years, M = 50.33, SD = 20.37) of 300 community-dwelling adults. Structural equation modeling identified a significant Age × Depression interaction in relation to visual search for measures of WP variability but not for mean reaction time. Older more depressed adults exhibited greater variability. WP variability in executive function and other cognitive constructs covaried, and the significant Age × Depression interaction with visual search was accounted for by WP variability in executive control. The findings suggest that age- and depression-related reductions in attentional resources may contribute to increased variability in visual search and that variability in executive control may be the mechanism underlying these effects.