The best way to figure out that you may start menstruating is to look for other signs of development, and ask your mother or older sister when they started. If my mother started menstruating when she was 15, will I start then too? Most likely you will. There is scientific evidence that show genetic factors to be a very important influence on the onset age of menstruation. How do you know when your first period is coming? Look for signs of your first period. First, your breasts may start to get bigger, hair may start to grow in the pubic area (between your legs) and, a little later, in your armpits. During this time you may notice a whitish discharge from your vagina. This is normal (and it's not urine, which comes from your urethra). A few months after that, you'll probably get your first period. When it actually begins, you might feel dampness on your underwear which is probably a few drops of blood. How long does a period last? It's different for everybody. Some girls menstruate for only 3 days, and some for as long as 7 or 8. The average is about 4–5 days. What if a girl never gets her period? Girls who reach the age 16 without menstruating may have primary amenorrhea (lack of menstrual flow). Primary amenorrhea requires careful medical testing, diagnosis, and therapy, so we suggest that you consult your family doctor. When does a woman stop menstruating? Women get periods until menopause, which is when menstruation and the ability to have children stops. In most women, it usually happens in their late 40s or early 50s. Is there any way to stop periods from coming? Menstrual flow is the result of hormonal action. Therefore, there is no medically safe way to stop menstruation or control the amount of flow.