According to Perez, Johns and just about everyone inbetween, Amazons don't have an approach to marriage, it's a concept that has no meaning to them. But I don't feel up to that rant just at the moment and will instead simply say that, yes, I imagine it's not Amazon standard to marry off 14-year-old girls to middle-aged men, but that doesn't really make "responsible adult at 16" any less likely, particularly considering Donna's privilege to hare off to Man's World and join the Titans (and the subsequent post-Crisis reinforcement by Byrne and PAD in re: Cassie).