In this article, we present and explain a bio-psycho-social model of successful aging with subjective well-being as a criterion of a successful aging process. We focus on physical activity because it is a crucial behavior. Physical activity can support successful aging in two different ways: first, due to its physiological and cognitive effects, and Second, an older person can enhance subjective well-being (SWB) while being physically active. The model points out that an older person can regulate SWB. To do this, an older person should set and pursue personally and culturally valued goals. The strength of the association between setting a goal and goal pursuance, respectively, and SWB depends on the extent a person is able to satisfy psychological needs (autonomy, competence, relatedness). But, the decision as to which goal will be set and pursued does not belong to the older person exclusively. The bio-psycho-social model explains that the chance to enhance SWB is restricted by personal dispositions (e.g., physiological constitution, psychological factors) and social–structural constraints (e.g., predominant stereotype of aging, facilities especially for target groups).