Observers often miss visual changes in the environment when they co-occur with other visual disruptions. This phenomenon is called change blindness. Previous research has shown that change blindness increases with age. The aim of the current study was to explore the role of post-perceptual stimulus processing in age differences. Therefore, the P3 component of the event-related potential was measured while younger, middle-aged, and older participants performed a change detection task under different task demands. Older adults detected fewer changes than younger adults, even when the task was very easy. Detected changes elicited greater P3 amplitudes than undetected changes in younger adults. This effect was reduced or even absent for middle-aged and older participants, irrespective of task demands. Because this P3 effect is supposed to reflect participants' confidence in change detection, less confidence in own responses may explain the decline of change detection performance in normal aging.