Jungle's Wild Beast 1971

Directed by Robert Ekhart

A kid goes missing. He ends up bonding with wild animals in the jungle, living with them and turning completely feral. So when they find him as a teenager and try to drag him back to the city to civilize him, he pushes back hard and fights it. None of the authorities' plans do a damn thing, except for the genuine kindness of a woman who's totally against exploiting the guy, and eventually, their efforts actually pay off.