The normal age of development for girls is usually 13 to 16 years old, and the exact age of development may vary due to individual differences. Girls usually start to develop around the age of 13-16 years old, and there are usually changes in tone, body hair, and genitalia, as well as the onset of menstruation. The tone of the voice and body hair of a girl’s body will change as she begins to develop. The tone of her voice will gradually rise, body hair will begin to grow, and her breasts will gradually develop. The genitals will gradually develop, the pubic mound will slowly rise, the labia majora will gradually enlarge and become pigmented, the vagina will gradually become wider and deeper, and the ovaries will begin to enlarge. After the girl starts to develop, there will be the first menstruation, usually after the first menstruation, the girl’s development speed will gradually slow down, and the psychology will also become more sensitive and fragile. Generally, as long as a girl’s developmental age is within the normal range, there is no need to worry too much, but if the development is too early or too late, it is recommended to actively go to the regular hospital for consultation, to clarify what causes, and follow the doctor’s instructions to deal with.