I think there is a definite difference in the “power” relationship between an adult student/client and trainer versus a child or teenager and trainer.
An adult is typically paying their own bills, owns their own horse, and can very easily go elsewhere for instruction if things don’t seem right.
A junior, on the other hand, typically doesn’t pay the bills her/himself; it’s usually the parents that do, so the rider has less control over the situation, especially if things are involved that they don’t feel comfortable talking about, or if they’re afraid they might lose the ride on a certain horse. Kids are also generally expected to obey their teachers do as they say in any situation, whereas adults are much freer to say “no” without repercussions. This dynamic probably also applies to young adults who aren’t technically minors but often still have parents paying the bills, etc.
I do think it’s a bit scary that SafeSport seemingly also applies to a fully consensual relationship between a trainer and adult student because of the supposed “power” differential (I realize that, although the details were deleted, that does NOT seem to be what was going on with the original person in question of this thread… this is a side note). While I think it’s generally a horrible idea from a professional standpoint for a trainer to get romantically involved with an adult student, and likely to end in a mess … I also think it’s a little disconcerting to a label that person as a “predator” for making a bad decision.