Baptism is the trigger that pulls the shun gun.
Your son is being manipulated by very clever propagandists.
Our daughter was was going through a rough time for awhile as a teenager, and a couple pioneer sisters took her under their wing. Unbeknownst to us, she was being "encouraged" by them to get baptized.
The one sister told our daughter that baptism is a "PROTECTION" against wrongdoing BECAUSE OF THE THREAT OF BEING DISFELLOWSHIPPED.
This is not protection, this is coercion to the extreme!!!
Imagine, being told that baptism can protect you from doing stupid things because your whole family and friends will never ever have anything to do with you again if you make decisions to do things they don't agree with, including having a doubt or question about the organization.
My husband and I have started watching "Sons of Anarchy" on Netflix, and it is amazing how much a motorcycle club or gang is just like a cult. Once committed, it's for life, or pay the (usually very extreme) penalty. You have to give all to the club and their agenda or else. In SOA, they kill you. In WT-land, they "spiritually" kill you, or view you as dead.
Remember, and tell this to your son, that baptism is the trigger that pulls the shun gun.
It cannot be undone. The WT considers baptism as a contract. What legality allows a minor to enter into a lifelong contract?? Tell him you appreciate his zeal and desire to serve God, and he can still do this, but without getting baptized. Jesus was 30. There is no rush. Jehovah knows his heart. Baptism is a personal dedication between an individual and his God, and is a step that an adult should make - Just like Jesus did.
Ask him if he think she is the same person he was when he was 5 years old, or 10 years old. Does he think he will still be the same person in another 5 or 10 years? There are so many things to learn and discover, and that includes personal development and growth too. If his desire to be baptized is still there when he is 18 or 21, at least he will be making an "adult" decision.
-- also, in the Bible Teach book, there is a paragraph which says people do NOT get baptized into an organization, but into a relationship with Jehovah. Why, then, does one of the baptism questions ask you if you understand you are entering into a relationship with Jehovah AND his organization??
I hope it all works out for you and your son....