"You are an occult detective?" John scoffs, since when barely adults are detectives. "Yeah, no. Give up the job, kid. it's not for immature people." He is not trying to be rude... Maybe a little rude, but he's mostly worried because young people think that they are ready for supernatural things and the knowledge of another world, but they are not, and he knows how dark things can get. He's as trying to look out for you. An act ot adult responsibility towards younger people.