Metabolism changes with age, just not when you might think. Most of us remember a time when we could eat anything we wanted and not gain weight. But a new study suggests your metabolism, the rate at which you burn calories, actually peaks much earlier and starts its inevitable decline later than you might think. Source 8n.
After the initial acceleration, the metabolic rate declines by 3% each year until age 20, when it stabilizes. From then on, metabolism remains stable until that magical (Average) age of 60, and then slows down.