Primary factors influencing an individual's BMR include age, gender, body composition, and hormonal balance. Typically, younger individuals have a higher BMR than older adults due to muscle mass decline with age. Men usually possess a higher BMR than women, largely due to greater muscle mass and less body fat. Muscle tissue burns more calories at rest than fat tissue. Additionally, hormones like thyroid hormones play a critical role in regulating metabolism. Understanding these factors can help tailor dietary and exercise approaches to individual needs.