Several factors can affect an individual's basal metabolic rate (BMR), including age, gender, weight, and muscle mass. Generally, younger individuals and those with higher muscle mass have higher BMR levels, as muscle tissue burns more calories at rest than fat tissue. Hormonal factors, such as thyroid hormones, and genetic predispositions can also influence metabolic rates. Lifestyle factors like diet and physical activity additionally play a role in determining BMR, making it essential for individuals to consider these when managing weight or planning diets.