Let me just wade in here.
If you'd like too much personal info I'll share with you that I was menstruating at 9.
In my first year of high school (11 years old) a girl in my year had a baby.

Medical issues are pretty much irrelevant.
Adulthood and maturity are measured by the collection and progression of experiences.
You can be a thirty five year old child if you've never known independence and responsibility.
The fact is there needs to be guidelines, they are there for a reason, and seeing as sex often equals kids, there has to be a limit.
It's a shame when a seventeen year old get prosecuted for sex with a person few days shy of their sixteenth birthday, but the law has to stay to stop fifty year olds having it away with fouteen year olds.