First, stop with the condescending bit. Puberty or when a girl start their cycle? Because it amounts to the same with your line of thinking.
Some girls start at 9 years old. What is the purpose of a menses? It sounds to me as if you are indicating that because something physiologically occurs, then it only makes sense that we are mature enough to marry. Not quite.
Physiological maturity does not equal emotional maturity or even intellectually ready.