12 years old, 20 days of menstruation.

Menstruation may not be stable, so the menstrual period may be very long, but must pay attention to medication conditioning, to prevent menstrual time is too long caused by anemia, mainly because of changes in hormone levels in the body. Menstruation cycle instability belongs to normal physiological changes. Some girls may come once or twice a month, menstrual interval time is relatively long, some more than two months or even half a year, a year later will gradually form the law.