This study aims to investigate how older adults react to a failed-inhibition error while performing a stop-signal task. That is, whether elderly people would exhibit enlarged post-error slowing and whether such slowing revealed an adaptive process, maladaptive process, or a mixture of maladaptive followed by adaptive processes. This study also addresses if the post-error process might further interact with a stimulus repetition effect based on the memory retrieval explanation. A group of 34 younger adults (age range 20–30 years) and a group of 34 older adults (age range 60–80 years) were included for the analyses. The results of the current study supported a mixture model by showing that older adults exhibited a larger post-error slowing than younger adults, and their post-error slowing was initially accompanied by deceased accuracy that then increased on the subsequent trial. Furthermore, such post-error slowing on older adults only occurred in the trial condition where the stimulus was repeated from the previous trial suggesting a memory-based process (a form of negative priming) involved in post-error processes. The implication of the current finding is that older adults might maintain the ability to detect and monitor the response error, yet their post-error adjustment might require a much longer time to start functioning well after the initial detrimental orienting response to the error and the entire process was memory-based.