The document provides an overview of concepts and theories of aging. It defines aging and classifies it objectively by chronological age and subjectively by changes in behavior, self-perception, and reaction to biological changes. It discusses concepts of aging including chronological, biological, psychological, social, and cognitive aging. It also outlines several biologic theories that attempt to explain the aging process from a physical perspective, including the programmed theory, gene theory, and free radical theory. In addition, it covers psychosocial theories like disengagement theory and activity theory that examine social and behavioral changes with aging. Developmental theories are also discussed, such as Erikson's theory of ego integrity versus despair in late adulthood.