At what age do girls generally get their first period?

Onset of menses?: Normal” puberty onset can range from ages 8-13 and takes, on average, 1.5-6 years to complete. Good documentation exists to establish that the average age of first menstruation in White U.S. girls has declined by several years, to an average of 13 years of age. It is not usually concerning for a girl not to have her first period until she reaches the age of 16 years.