The average age for a girl to get her first period is about 11 to 14 years old, but some start much earlier or later. It is perfectly normal for a girl to get her first period anywhere between the ages of 8 and 15.  Most girls do not start their periods until they weigh at least 100 pounds. If you are a bit behind your friends with growth spurts, your period may start a bit later, too. It's nothing to worry about, so just be patient.  If you haven't had your first period by the time you are 15, or within three years of when your breasts first started to develop, you should consult a doctor. If you get your period much earlier or much later than your friends, you might feel different than everyone else. You might get your period when you are 9 or 10, or not until you are in your mid-teens, and both are perfectly normal! It's important to understand that all girls get their periods at different ages. Genetics play a huge role in determining when you will get your first period. Try asking your mom and sisters when they got their first periods. While you're not guaranteed to get yours at the same age they did, there's a good chance that you will be around the same age they were.

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Write a summary of the previous text in Vietnamese:
Độ tuổi trung bình. Đừng so sánh bản thân với người khác. Hỏi người thân là nữ.