Remembering to execute intended actions in the future upon encountering specific target events is referred to as event-based prospective memory. In this research, we examined how individuals manage competing goals and execute delayed intentions and how this cognitive ability evolves along adulthood. Our theoretical groundwork was based on task switching and two processes, retrieval mode and target checking, underlying strategic monitoring of PM retrieval. We compared young (ages 19-24) and old (ages 59-79) adults (N = 40) on pure and mixed blocks of trials where they decided if a digit was bigger or smaller than five or odd or even. Target cues were letters that appeared on each side of the number. Results of PM performance were unexpected, showing no age difference. Entering retrieval mode and having high PM performance come at a cost for the ongoing task, especially for old adults, demonstrating that it is more difficult for adults to manage multiple goals and intentions...