I think it's more squicky if the genders were reversed because if the young one was a girl and she had hit puberty already, she would have been expected to bear a child sooner (as in, as early as 13), while in this situation no one is expecting the couple to even consummate. I don't know the specifics of their particular culture; maybe they wait until the girl is over 16 at least, but that is what my mind jumps to.