Age affects physical fitness capabilities primarily due to changes in muscle mass, bone density, and metabolism. As individuals age, muscle strength and flexibility often decline, making some physical activities more challenging. Bones may become less dense, increasing the risk of fractures and osteoporosis. Moreover, metabolic rates tend to slow down, affecting weight management and energy levels. However, regular exercise can mitigate these age-related changes by enhancing strength, balance, and cardiovascular health, making it crucial for older adults to maintain an active lifestyle.