In a population unselected for aerobic fitness status, aerobic fitness(˙VO2max) and its interaction with age were used to predict performance on several cognitive measures known to be affected by chronological age. It was hypothesized that, in particular, cognitively demanding tasks would be sensitive to aerobic capacity. Healthy subjects between 24 and 76 yr of age (N = 132) were recruited from a larger study into determinants of cognitive aging (Maastricht Aging Study-MAAS). All participants took part in a submaximal bicycle ergometer protocol and an extensive neurocognitive examination, including tests of intelligence, verbal memory, and simple and complex cognitive speed. Participants engaged more hours a week in aerobic sports and felt healthier than the nonparticipants of the same age did. No group differences were found in the basic anthropometric characteristics height, weight, and BMI. Two of four subtasks that reflect complex cognitive speed (Stroop color/word interference and Concept Shifting Test) showed main and interaction effects with age of aerobic capacity in a hierarchical regression analysis, accounting for up to 5% of variance in parameter score after correction for age, sex, and intelligence main effects. These findings fit well within a moderator model of aerobic fitness in cognitive aging. They add to the notion that aerobic fitness may selectively and age-dependently act on cognitive processes, in particular those that require relatively large attentional resources.