Age and fitness levels significantly affect metabolic rates. Typically, metabolism slows with age due to a decrease in muscle mass and hormonal changes. This reduction means that older adults burn fewer calories at rest compared to younger individuals. Additionally, fitness levels influence metabolism; those who are physically active often experience a higher metabolic rate due to increased muscle mass and overall energy expenditure. To counteract age-related metabolic decline, regular strength training and aerobic exercises are essential to help preserve muscle mass and maintain a more active metabolism.