with all due respect, most of the books listed above are quite good orthodox Catholic spirituality, but written in an archaic English, hard to understand, and unlikely to appeal to teens or young adults. Except for CS Lewis of course who is very accessible, and Screwtape would be a great place to start.
To counter the ideas he is getting in these horrid books, try Fr. Mitch Pacwa’s tapes on the New Age (from EWTN) and We’re on a Mission From God (Ignatius) which has brief, true, orthodox presentation in modern idiom on major aspects of the faith and moral issues intended for youth, especially college age. Also anything Amy Wellborn (OSV) and Fr Stan Fortuna, which are written especially for youth addressing their concerns and giving authentic Catholic teaching. Fr. Stan has his own website, which I can’t find just now, but somebody out there must know it.