When I grew up in the 50s in rural US (well water with electric pump, solar water heating with a black tank on the roof of the shower, and wooden outhouses), several households shared outhouse facilities. Adults used "single" outhouses, but there was a three-seater for the children. Male-female didn't matter, but the custom was that adults needed their privacy, children didn't. As I recall, the restroom change occurred at menarche. There was probably a time for boys to go to the separate outhouse, too, but men generally urinated in situ behind some tree, but never exposed his privates to anyone. If you saw a guy's back and he was facing a tree with his hands "down there," just leave him alone.