As the global population ages, distinguishing between the effects of chronic diseases and inherent aging challenges becomes paramount. The intersection of geriatric neuropsychology and gerontology provides a comprehensive framework to navigate these complexities. We will explore the foundational aspects of geriatric neuropsychology, surveying prominent theories of brain aging, structural and functional changes, and the intricate relationship between aging and neurodegenerative diseases. Acknowledging the relevance of frailty as a critical marker, the chapter emphasizes the importance of a comprehensive geriatric evaluation to guide nuanced interventions. A pivotal focus is then directed toward non-invasive neuromodulatory treatments, particularly transcranial magnetic stimulation (TMS), and its application in mitigating age-related cognitive decline. This exploration is contextualized within the broader framework of the medicine of complexity, recognizing the interconnectedness of various physiological and psychological factors in aging.