The age at which girls menstruate ranges from 11 to 16 years old, and varies due to the different physical qualities of individuals. In the 11 to 16 age group, the reproductive organs such as the uterus, ovaries and vagina gradually develop and mature, and the follicles in the ovaries begin to mature, so the conditions for the formation of menstruation tend to be perfected, so the endometrium is stimulated by estrogen and progesterone, and will usually have menstruation at this stage. The exact time of menstruation may fluctuate depending on the development of each individual. If a person does not have menstruation after the age of 16, there may be abnormalities such as uterine dysplasia or endocrine disorders, so it is necessary to go to the hospital in time to complete the relevant examinations and under the guidance of the doctor to carry out treatment.