The time of epiphyseal closure differs for boys and girls with normal growth and development. Generally, the epiphysis closes at the age of 13 for girls, and two years later for boys than girls, at the age of 15. At the age of 8 for girls and 9 for boys, the hypothalamic-pituitary-gonadal axis starts to develop and the secondary sexual characteristics start to grow. The first sign of puberty in boys is testicular enlargement, and the first sign in girls is breast growth, and the growth of bones sensitive to sex hormones will accelerate. The end of puberty for girls is marked by the first menstrual period, and the epiphysis of girls closes after about six months, reaching a lifelong adult height. Boys, on the other hand, tend to be two years late due to a relative lag in the initiation of puberty, so the epiphysis usually closes around the age of 15 for boys. Of course, if due to delayed puberty, it is possible for both boys and girls to have their epiphyses close at a relatively wrong time. However, if precocious puberty occurs for some reason, there is a gap between the actual age and the accelerated growth of the bones, and in some cases, the bones grow too fast and the bone age exceeds the actual age by two or even three years, so that the epiphysis may close early. Early closure of the epiphysis caused by precocious puberty may affect the adult lifetime height.