Successful aging has become an increasingly popular concept in light of population aging worldwide. Understanding resilience, the tendency to recover from life stressors, is integral to identifying factors that facilitate successful aging in individuals. Yet, current literature on resilience, and the related notion of frailty, lacks a common framework and clarity of concepts. We develop and describe a simple dynamic model that produces a wide range of life course trajectories of functional ability in individuals based on a few, explicitly defined factors.