Previous research has demonstrated that episodic future thinking (EFT) can enhance prospective memory (PM); however, its effects on older adults have been less explored. This study examines the impact of EFT training on PM in both older and younger adults under varying delay intervals. Experiment 1 employed a 2 (EFT training: present vs. absent) × 2 (age: younger adults vs. older adults) × 2 (delay interval: 5 min vs. 20 min) between-subjects design. The results revealed a significant main effect of EFT training (p < 0.001), indicating that such training improves PM performance. Among younger adults, a significant difference in PM performance was found between the trained and untrained groups (p = 0.03), while among older adults, this difference was only marginally significant. This suggests that the facilitative effect of EFT training is more pronounced in younger adults. Additionally, there was a significant main effect of delay interval (p = 0.01), with shorter intervals yielding better PM performance than longer intervals. Experiment 2 focused on the impact of specificity in EFT training on PM in both age groups. A 2 (training: specific vs. non-specific) × 2 (age: younger vs. older adults) × 2 (delay interval: 5 min vs. 20 min) between-subjects design was used. Results indicated that older adults in the specific training group outperformed those in the non-specific training group (p = 0.03), whereas no difference was observed among younger adults. This finding suggests that specific training is more effective for enhancing prospective memory in older adults. Moreover, older adults exhibited differences based on the delay interval, with a 20 min interval impairing performance (p = 0.04), while younger adults showed no difference between the two intervals. These findings will be discussed in relation to the Multiprocess Model and the Preparatory Attention and Memory Processes Theory.