OK, Ethan, let's throw Romeo and Juliet in the garbage can... they could have held off on their inappropriate passions, for five years.

They were close enough in age that reasonable age-of-consent laws with "Romeo and Juliet exceptions" (how conveniently named) would mean there was no legal problem.

If you strip away all the art from the story, then just about all the modern psychological advice in the world would suggest that eloping with someone where the two families really do not get along AT ALL and at that young age is a poor gamble for happiness. Not a legal problem, but a really bad idea.

If they want to mess around and have fun with sex, that's fine with me and with liberal sex-positive folks (who are still adamantly against adult-child sex).