You're probably the only person who would describe the film as "a completely standard coming of age tale". I mean, on what planet? Again, I had the same initial feeling of being underwhelmed but the film's uniqueness was still pretty apparent. And I really do appreciate how little they actually spelled out for the audience. Rather than "quiet" I'd use Tony V's favorite adjective to praise a film: restrained.
But yeah, the teenage actor didn't really seem like the adult actor in terms of both appearance or behavior but that can be explained away by what had transpired between the 2 point of time so I don't really think it counts as "cheating".