Just another example of the “I can pick and choose, and I can infallibly interpret scripture” camp. The website’s author has a good intent but faulty research. He really just wants masturbation to be good and healthy. His interpretation of the Gnostics is actually too limited. They were more against “the flesh” than he realizes. He doesn’t know the idioms of Jewish history when he says that masturbation isn’t “spelled out as a sin.”
He wants boys to understand their bodies, but with his lack of understanding of God’s design, he himself doesn’t understand the nature of the body. Pray for him and anyone who reads his site. There have been those people for centuries who have tried to rewrite history to legitimize sexual sins. The internet has just put them right in our faces.
In my opinion his info is worth ignoring. Other people might say to take on his claims and try to set him straight. Only do so if you are rock solid in your understanding of Catholic teaching.
Blessings in whichever direction the Lord leads you!