Prospective memory (PM) is the ability to remember to perform an action at a specific point in the future. Regarded as multidimensional, PM involves several cognitive functions that are known to be impaired in normal ageing. In the present study we set out to investigate the cognitive correlates of PM impairment in normal ageing. Manipulating cognitive load, we assessed event- and time-based PM, as well as several cognitive functions, including executive functions, working memory, and retrospective episodic memory, in healthy participants covering the entire adulthood. We found that normal ageing was characterised by PM decline in all conditions and that event-based PM was more sensitive to the effects of ageing than time-based PM. Whatever the conditions, PM was linked to inhibition and processing speed. However, while event-based PM was mainly mediated by binding and retrospective memory processes, time-based PM was mainly related to inhibition. The only distinction between high- and low-load PM cognitive correlates lies in an additional, but marginal, correlation between updating and the high-load PM condition. The association of distinct cognitive functions, as well as shared mechanisms with event- and time-based PM, confirm that each type of PM relies on a different set of processes.