@maxdancona,
See? your ideas are based in our current culture.
In the past, a 17 years old was getting "old" already to get married. Women used to get married at 13, 14 years old and forward. Still there are cultures in other nations where they allow 14 years old women to get married. Check some parts in India as an example.
The Western culture in the past also allowed the marriage of young 13 years old women.
Today, the Western culture has changed, the age of a woman to be married has been raised to 18 years old by herself or 17 with the consent of parents in many places.
The change is not because the young woman is not an "adult" at 13 years old, but the idea is to give her a chance to finish school, perhaps to start a career, etc.
But, BIOLOGICALLY SPEAKING, when a girl starts her menstruation she has become a woman, biologically an adult woman capable to conceive and be a mother.
About your points as responsibility, etc. you are all right, such is part of our culture, but when is about "scientific facts" the girl who starts menstruation is already a woman.
I know you don't like the scientific fact, but my position stands in what can be proved as a true in science.