Despite the well-documented and publicized benifits of participation in physical activity, recent research points to a declining involvement in physical activity with advancing age, This paper suggests that this decline may be attributable, in part, to the age grading of physical activity participation. A conceptual framework for understanding the age grading of human behavior is presente. Preliminary data are discussed that reveal that young people have clear, ageregulated social prescriptions about the exten to which people should be involved in physical activity as they grow older.