Biologically it makes zero sense to try to breed with a partner not physiologically ready to produce offspring. Thus, it's exceedingly easy to label it, scientifically so, a mental disorder. However, once the partner is biologically ready to reproduce, it becomes a more muddy subject dependent on ethics. It's only due to ethics that the legal marriage age climbed up to 18. I could see hebephilia labeled a disorder these days, but with ephebophilia it's never going to happen. Just the differing ages of consent between countries (or even states) alone would make it laughable.