A person's metabolism tends to drop by approximately 1-2% per decade after age 20.
Typically, a person's metabolism, measured as Basal Metabolic Rate (BMR), decreases by about 1-2% per decade after the age of 20. This decline is largely due to factors like reduced muscle mass, hormonal changes, and a decrease in physical activity levels as people age.
However, these numbers can vary based on an individual's lifestyle, genetics, and other health-related factors. Regular exercise and maintaining muscle mass can help mitigate some of the metabolic decline associated with aging.