Girls typically get their first period, known as menarche, between the ages of 10 and 15, with the average age being around 12 years old
. Most girls start their periods about two years after their breasts begin to develop, and they may notice vaginal discharge about 6 months to a year before their first period
. The onset of periods has been occurring slightly earlier over recent decades; for example, in the U.S., the average age has shifted from around 14 a century ago to about 12 now, which is roughly six months earlier than 20 or 30 years ago
. It is normal for periods to start anywhere within this range, and various factors such as genetics, body weight, stress, and physical activity can influence the timing. If a girl has not started her period by age 15, it is advisable to consult a doctor to rule out any underlying health issues
