By recording the feedback-related negativity (FRN) in response to gains and losses, we investigated the contribution of outcome monitoring mechanisms to age-associated differences in probabilistic reinforcement learning. Specifically, we assessed the difference of the monitoring reactions to gains and losses to investigate the monitoring of outcomes according to task-specific goals across the life span. The FRN and the behavioral indicators of learning were measured in a sample of 44 children, 45 adolescents, 46 younger adults, and 44 older adults. The amplitude of the FRN after gains and losses was found to decrease monotonically from childhood to old age. Furthermore, relative to adolescents and younger adults, both children and older adults (a) showed smaller differences between the FRN after losses and the FRN after gains, indicating a less differentiated classification of outcomes on the basis of task-specific goals; (b) needed more trials to learn from choice outcomes, particularly when differences in reward likelihood between the choices were small; and (c) learned less from gains than from losses. We suggest that the relatively greater loss sensitivity among children and older adults may reflect ontogenetic changes in dopaminergic neuromodulation.