Hello Finatic - two resources that may help your son - Handbook of Catholic Apologetics by Peter Kreeft - it may be above his reading level but it sounds like it might not be, judging from his eagerness to engage others and seek the truth of things. If he works through it with a knowledgeable adult advisor (catechist? parish priest?) he may come away with a deep and strong appreciation of the faith that will stand up to any serious intellectual challenge.
A second resource has to do with faith and science, specifically aimed at high school students: the Faith and Reason series (Fr. Robert Spitzer SJ) which examines evidence for God from physics and philosophy. I was a volunteer with the project several years ago and I have shown the 5-DVD series to my class with thoughtful results. The series was based on Fr. Spitzer’s book, New Proofs for the Existence of God, a highly compelling, if intellectual, read.
Here is the link for the Kreeft book:
and here is the link to the Reason Series program:
Adolescence is such a time of fierce spiritual battle - I teach in a grade 7-12 Catholic school - and the stakes are so high. I applaud you so much for being so involved in helping your son in his honest search for the highest truth there is.