This review summarizes current evidence on the convergence of medical rehabilitation, functional geriatrics, and longevity medicine. The evolution of geriatric care from a disease-centered model to a functional approach based on the concepts of healthy ageing, intrinsic capacity, and comprehensive geriatric assessment is discussed. Particular attention is paid to the contribution of geroscience to modern longevity medicine and to the growing role of biological ageing biomarkers as promising indicators for evaluating rehabilitation outcomes. Current concepts of rehabilitation potential are analyzed, emphasizing the importance of physiological reserve together with cognitive, psychological, adaptive, and social resources. The available evidence also highlights the increasing significance of psychological rehabilitation in promoting healthy ageing through improved adaptability, social engagement, personal growth, and psychological well-being. The convergence of medical rehabilitation, functional geriatrics, and longevity medicine provides a methodological framework for developing comprehensive, personalized rehabilitation programs aimed at preserving functional independence, extending healthspan, and improving quality of life in older adults.