Girls are generally fully developed around the age of 16-20, with large individual differences. The puberty of girls is generally 10-18 years old, at this stage under the action of sex hormones, the growth and development of girls accelerated significantly, height and weight increased substantially, secondary sexual characteristics began to appear, and the reproductive organs developed and tended to mature. During puberty, the first sex characteristics of girls are mainly the development of the reproductive system. Changes in the external genitalia include the thickening of the labia majora and the enlarging of the labia minora, etc. The internal genitalia change mainly to the vagina. Changes in the internal genitalia include an increase in the length and width of the vagina and an enlargement of the uterus. It is normal for girls to have their first menstruation at the age of 10-15. The secondary sexual characteristics of girls mainly include breast augmentation, widening of the pelvis, thinning of the voice, increase in subcutaneous fat, and the appearance of armpit and pubic hair. Due to individual differences, girls usually develop fully between the ages of 16-20.