The prevalence of cognitive impairment and dementia in the ageing population emphasises the need for strategies to mitigate cognitive decline. While research on Alzheimer’s Disease (AD) has focused on early risk factors, less attention has been paid to protective factors such as cognitive reserve (CR) and cognitive control (CC). Methods: This review examines age-related changes in the prefrontal cortex (PFC) in healthy ageing and cognitive impairment. We analysed studies using Stroop and Simon tasks in conjunction with EEG, EEG/ERP, fNIRS and fMRI. Results: Of the 1411 articles reviewed, 49 studies met our criteria. The results suggest that the Stroop and Simon effects are essential for distinguishing between healthy ageing and cognitive impairment. Increased activity of the PFC supports task performance, especially in cognitive ageing. However, when compensatory mechanisms fail, deficits in Stroop and Simon effects may indicate cognitive impairment and reduced activation of the PFC. Conclusion: This review emphasises the critical role of CR in attenuating age-related cognitive decline and highlights the importance of the PFC in maintaining CC.