Really.  The above post is really uneeded.  I am an 18 year old male, who lived with a very conservative family.  I was never shown or taught anything.  I went onto the internet to discover everything.  I think that you should talk to him about masterbation.  ALL OF IT!!  You may even go as far as to teach him a few things.  Ask him if he has any questions.  Better for him to learn from his father someone he trusts, than the internet.

Good Luck