In the field of developmental and educational psychology, much of the research on cognitive processes of older adults has focused on the disorganization and decline of mental functions. Such an approach, however, tends to overlook the potential for learning and psychological development in seniors when they engage in activities that draw on competencies acquired in earlier phases of their life. Adopting a sociocultural and dialogical perspective, this paper examines the competencies mobilized and further developed by seniors involved in volunteer work within associations in the French-speaking part of Switzerland. More specifically, we provide a detailed analysis of how one volunteer’s competencies are enacted in her engagement within an association. By highlighting the different dimensions of the competencies she brings into play, this study contributes to a definition of competence grounded in a sociocultural psychological framework, as well as to a discussion of the methodological conditions required to study it. More broadly, this paper advances our understanding of how older adults mobilize their competencies in practice and shows the essential role these competencies play for society.