Why not translate this as "the young man sees a pretty girl"? Or, "the youth", if we want to stay more literal? "Teenage boy" just sounds so clunky that I doubt a native English speaker would use those words.
I don't think so, but in Hebrew נער/נערה is a more specific term and doesn't refer to small children.
The lad sees a pretty lass. Near enough to a literal translation, I think.
I agree with Dov. Nobody says the teenage boy sees a pretty teenage girl. It's assumed, unless he's a pervert, he's looking at someone in his age group.