I agree with the above with the caveat that he doesn't tell you or anyone else that is is irrelevant and you help him find someone else to argue with. The meaning of life conversations that are part of the teenage/young adult years are tiresome for older people and an engaged partner is essential.
For the op my sons Sunday school teacher lent me acouple of books the other day "100 questions kids as about God" and "100 questions kids ask about the bible". They probably aren't any good to a Catholic but you could look.
