Yes, your metabolism declines as you age. It's not that 18-year-olds can eat whatever they want and not gain weight, it's that 18 is the age where most people s

Yes, your metabolism declines as you age. It's not that 18-year-olds can eat whatever they want and not gain weight, it's that 18 is the age where most people settle into eating habits based on their equilibrium at that time. As their daily expenditure slows by roughly 150 calories per decade, they don't adjust their eating habits and slowly gain weight.