In the United States, menarche (onset of menstruation) typically occurs around age 12, although some youngsters start puberty when they are only eight or nine, others when they are well into their teens.
Menarche may be the first outward indication of your blossoming adulthood.
Once menarche (the first period) begins, you may feel frightened, shocked, and confused.
Girl puberty consists of many changes, from the beginning of menarche to the rapid social and cognitive developments taking place in the brain.
For girls, the hormone estrogen substantially increases, leading to breast development, a curvier figure, and menarche, which is the first period.