I wonder why a girl's vagina bleeds at the age of 13 - 25
It goes until later in life when you hit menopause...50's I think
Periods start when a girl is able to have a baby(though your body is still not completely ready, emotionally and physically, until your 20's probably)
It is preparing the body for conception each month by lining the uterus with blood and tissue.
The blood is the blood that would nourish a growing fetus if the girl was to become pregnant, if not it is simply flushed out.
your periods last a lot longer than 25 lol think... about 50 lol