Agreed on most points. 

" If a woman is menstruating, they are ready to have sex and procreate." --- this isn't actually accurate. A girl may begin menstruating at 9-10, but her hips might not widen until 16 or 17. If she were to have sex and procreate, she's much more likely to die in childbirth or have to have a c-section. Unfortunately menstruation doesn't actually equal readiness to reproduce even biologically. 

Women in history usually didn't menstruate (on average) until their mid-and-later-teens. They were sometimes married off earlier, but often didn't have sex or give birth until later. The earlier they had children, the shorter their life expectancy, and the life expectancy of their children. Richer/wealthier/high class women tended to get their periods earlier, presumably due to better nutrition. 

Our diets and resource-rich lives (on average) have led to earlier and earlier menstruation - the average first period is now at age 12 (there are indicators that the added hormones in milk, meat and dairy are speeding that process up). It doesn't necessarily mean we're ready for sex/pregnancy. 

I had my first period at 14. I also started college, met a guy who was 25 but I had a LOT in common with, and started a friendship that became a courtship - and at 15 I wanted to have sex with him. He refused me due to my youth (and laws), and so we maintained a close friendship that eventually led to a sexual relationship when I was 17. As I say - I was capable of consenting much earlier than I actually had sex. The ability to consent includes the ability to refuse or withdraw consent. 

Anyway, I agree with your points generally, and think utilizing hard age lines for Age of Consent laws is a terrible way to go about things.