A youngster is also sensitive to the metal. My preference is an iron mouth and as previously mentioned let the horse just pack it around. Start with about 15 min day then gradually increase it to several hours. Offer hay and let him figure out how to eat it. Be sure to check on him frequently. This will help toughen his gums before you ride him. You may opt to bridle him with reins, again, new weight on his mouth and ride in a knotted halter. Teach him to move his head with groundwork until he will willingly bring his nose around almost to his shoulder, first with the halter, then with the bit. Don't hasten this process as it can be real tough to undo. Horses move in to pain so if his mouth hurts he will brace against your requests.