Why does menstruation start during the age of puberty and not before it?
Puberty and menstruation are triggered by estrogen, of which
high quantities are released by the Pituitary gland in the
That's a bit like asking why it doesn't get dark until sunset.
Puberty is the name for the phase when the body is growing
big/mature enough to be able to become a parent. And for
girls/women, they can't become parents unless they're menstruating.
So for girls/women puberty and menstruating are tied together.