I am not sure that the DL is too long. If he stood straight and pushed that left arm out a bit I think he would be on the money.
He is leaning his head down into the peep, if he still does this AFTER you adjust the DL/position, move the peep up a bit so he is looking straight into it. I would also encourage shooting off the tip of the nose, not the side. I see both but the tip is a more consistent spot (less flesh there).
Also, tell him to relax those front fingers. It is hard to tell by a picture but those babies need to be limber and free of tension.
Shorten up the release some, he is using the tip of his finger and should be using the first crease. Using the tip will encourage punching the trigger. I suggest at least the first crease, lock in the finger and actually use back muscles to pull through the shot.
Nice to see the young man with a bow in his hand. Kudos to the adults that support their kids.