"L'enfant d'eau", Canada (in French), late 1990s.
The situation there is very significant as the girl is clearly shown to be the interested party.
Some people question how the adult guy is, well, if you didn't want spoilers, I won't give them. But the features of the guy which some would be dismissive or rejecting of, are necessary to portray the girl as Not A Victim.
That's why I consider this relatively obscure movie as one of the top GL movies ever.