Metabolic rates begin to slow at which life stage?

Metabolic rates begin to wane down at a different pace for both males and females. Men tend to have a slower metabolic rate at the age of thirty, while women experience this at the age of twenty-five. The slow metabolic rate is caused by the body's natural way of deteriorating as it ages. When metabolic rates are slow, people are advised to expend more energy and take in lesser calories so as to maintain physical characteristics of the body. But on rare occasions, others tend to have slow metabolic rates in later parts of their lives. This is mainly because of factors like heredity and the lifestyle a person is making.    

So that you don't get baby's but also prevents stis such as hiv