I assume he has had some pretty good growth spurts. My concern is that with rapid growth his elbow may be a bit soft and he has the size to actually do some damage with the curve. I would suggest concentrating on developing more powerful movement patterns for his fastball and working on a pronated type of change until he is at least 15.
To start I would concentrate on his posting leg foot. From the stretch I would have him set his foot perpendicular to the stride path. he should then rotate his posting knee inward just enough to feel his weight shift to the inside of his posting foot (right).
The weight should feel like it is in the arch or heelward. You can see that his weight is very much on the ball of his foot early in his delivery. This allows the heel to rotate towards the plate and robs him of both direction and power. He has a gift in size if his growth continues. Take care of him.
Best of luck,