on average girls start puberty between the ages of 9 and 14 but some will start to develop breasts or pubic hair by age 8 and a small number will start to mature before age 7the technical term for this is precocious pubertygirls are five times more likely than boys to develop precocious pubertyn average girls start puberty between the ages of 9 and 14 but some will start to develop breasts or pubic hair by age 8 and a small number will start to mature before age 7