Scientific evidence of the benefits of physical activity (PA) as people age, particularly after age 50, is mounting at a time when population aging—especially in France—is becoming a major public health issue. These benefits, which affect all the systems and organs of the human body, enable “successful aging” but, above all—and this is the central focus of current public health policies—they help combat “frailty,” maintain independence, and prevent dependency. Drawing on a bibliography dating from 2008 onward and based primarily on reviews and meta-analyses, this review focuses on the benefits of physical activity for the cardiovascular, musculoskeletal, neurocognitive, and immune systems, and on their impact on quality of life and life expectancy. The potential harms of improperly conducted physical activity, particularly on the cardiovascular and musculoskeletal systems, are also discussed. A brief overview of current recommendations regarding physical activity for health in older adults is provided at the end of the review.