Basic information description Complete absence of menstruation in a young woman who is at least 16 years old, or at age 14 with a lack of normal growth or absence of secondary sexual development. It is a rare disorder, as over 95% of girls have their first menstrual period by age 15. Most girls begin menstruating by age 14, average age is 12 years, 8 months. frequent signs and symptoms Lack of menstrual periods after puberty. causes A failure of certain complex body functions that...