I would say that if he is REALLY serious about it and he is old and mature enough to handle what it would take then tell him to get outfitted as soon as possible. Tell him that when ever you go to the local range or 3D shoot or just practice in the back yard that he should come with you. Do a lot of shooting at the pro shop where the "pros" can help give him a lot of instruction and take some of the pressure off of you so that you can get in some shooting time also. After he has all of the basic skills then take him to the 3D shoots or just practice in the yard at unknown distances so he can learn to judge distance.

Explain to him that if he really wants to do this he will need to put in the time to practice as much as possible. Let him know up front that if he is not willing to put in the time then he will have to wait until the next season to put his newely learned skills to the ultimate test.

If he is willing to do what it takes I think you should be OK with your time frame.

Basically made it abundantly available to him to practice with you.