What age is normal for a teen getting her first period?

9-16 years. Average age as mentioned is 12 to 13 but that does vary. Can depend on the mothers age of her first menses, also can depend on ethnicity for unknown reason girls of color more often start earlier usually age 9 or 10. So it can be as early as 9 and as late as 16 years old. However usually first there are signs of breast development and pubic hairs prior to any bleeding.
Ave in US 12-13. The expected range in the us is 9-15 with about 1% occurring earlier or later.