Re: Need help with some advise for 13 yr old
First thing, get him a wrist sling! He is death-gripping the bow because he's afraid his new plaything is gonna hit the concrete!
More on that in a minute...
His draw-length is spot on—the nock point should be equal to the outer edge of the eye. The line of sight should be close to parallel with the bow arm (he's very close)
He does need to relax the release arm and that elbow. If that release is adjustable shorten the throat of it where it is at the knuckle closest to the palm (it looks like he may have to stretch it out and is using the fingertip). Getting it deep will allow him to have more of a surprise release and will help discourage "punching" because he is having to stretch for it.
His stance appears to be closed (it could be just the camera angle) on his lower half, but open on the upper torso—this will put everything in a bind if that's the case. Most people shoot and find the most comfort with a very slight open stance. I like putting people up against a wall (especially kids), so they can feel what a square stance is, from the feet to the shoulders—it also encourages them to stand up straight, which will allow proper support of the skeletal structure and will allow for easier activation of the right rhomboid when/if he decides to start incorporating back tension as the means to start the shot sequence. Whatever he does, make sure the feet, hips and shoulders are pointed together in the same direction for the most part.
The biggest thing by far is the grip and his bow arm. The diagram tree ghost provided is spot on and here it what it looks like in action.
See the 45degree slope of the knuckles