Ok, I'm not a pro and I will tell you now that I start my dogs a little earlier than most. If you want to keep that young pup on birds then start him retrieving frozen birds to help with the chewing. You may run into trouble as he may not want to retrieve a frozen bird. I have a young Springer that will hardly even pick up a down bird until he has gotten to chase a shackled one. It's like a light comes on when he gets to chase that bird then he is non slip.
When I have dog that is hard mouthed I will use a slightly larger frozen bird like a chukar. It's harder for them to chew when the mouth is so full. If they still want to chew I'll wrap that bird with a strand of barb wire. It works. The key is not to be in too big of a hurry. Know that the pup is going to make mistakes and give him many chances to do it the right way.
You can start a dog young as long as you are not affraid to handle them easily and give a little. Or you can wait until their older and miss letting them have all that fun. Let him be a kid and enjoy him. If he chews birds then don't let him retrieve them unless you are right there to get the bird before he can eat it then work with him in his off time with frozen birds and wire. One thing to consider is how long you let him hold the bird in the field. If he has it for a while or you let him run a round with it then it's kind of natural to start chewing on it. Try turning your back to him and walking or running away while calling him in. As he gets to you then reach out and take him in. Pet him and praise him before taking his bird. HAVE FUN!!

Tim