I didn't read through all the responses so I am sorry if this is a duplicate answer.

I was in the same boat this year with my 13yr old son. I will be very honest, I discouraged him from shooting more then 10 arrows a session with 2 sessions a day max. He had yet to develop the strength and stamina in his muscles to shoot many more shots then that. I did not want him getting in to bad habits due to him having to compensate. He fought very hard to shoot more arrows and I know if I would have let him he would have shot all day long. We made the short sessions count, plain and simple. As far as accuracy, let him prove to you how far he can shoot. He may be a natural. My son was dead on at 10,20,30 yards. Any more then that and he had issues. I limited him to 20 yard shots in the woods knowing that he had 30 yards down. He end taking a 6point on his 3rd sit of the season.