Prospective memory (PM) refers to the ability to remember to carry out a delayed intention in the future. Monitoring is the controlled surveillance of the environment for PM cues, which indicates the right moment for the execution of the PM intention. The present study investigated younger and older adults' ability to flexibly engage in monitoring process. Participants performed an Eriksen flanker task as ongoing activity, solely in the control condition, and with a concurrent PM task in the PM condition. In the delayed PM condition participants received the PM intention, but with the instruction to only carry it out later. Here, target cues appeared unexpectedly early, allowing to examine participants' attentional resource allocation to monitoring when PM cue is not -yet- relevant. Results indicate that individuals flexibly invest resources in monitoring processes. This pattern is similar in both age groups: older adults use monitoring strategies comparable to younger ones, and engage in monitoring only when that is necessary. These findings suggest that monitoring strategies in PM remain intact with older age.