bballman- Your son has very sound mechanics and looks to have been taught many of the general pitching concepts very well. If the velocity numbers you provided are consistent then I believe he should have no problem finding his way onto a college roster.
I am a fan of separating the body into different aspects in order to piece a delivery together step by step. A lot of big league pitchers have many different kinds of deliveries, but 99% of them have their body parts work synonymously with one another nearly perfectly.
Your son does an excellent job of leading with his hip and providing a strong base for maximized torque with his lower body, like I've indicated is desireable in my previous posts. However, he has what a lot of instructors refer to as a "lazy" glove side. If you freeze-frame your Youtube clip at 00:23 seconds, you can see that his glove is down by his knee and his front elbow is parallel with his chest. Ideally, I'd like to see his elbow almost parallel with his front shoulder (think of using a scope on a hunting rifle stationed on a tripod, with the elbow being aligned so that it is similar to a scope). Also, the thumb down concept on the glove at the point where the ball is at its peak 90 degree angle (like it is at the 00:23 second mark) will allow for a better ability to turn the glove in towards the chest and enable the throwing shoulder to come through the throwing zone (I don't know if it is actually called a throwing zone, but people call the point of contact for a batter a "hitting zone" so I'll call the point of release for a pitcher a "throwing zone").
Your son does an outstanding job of getting his chest over his front side and into an ideal position for a true finish on his pitch. However, if he can provide a stronger glove arm, like I illustrated, then the symmetry of the posterior scapular load will be much stronger. The posterior scapulars are the muscles in the back of your shoulders, and the correlation of the adverse movements of both the left and right scaps in unison provide extra torque generated for velocity. In an attempt to stray away from the kiniesology aspect of things, I'll try to simplify my point in more understandable terms. If you put both of your arms up in the air at a 90 degree angle bent at the elbows and move them backwards, you will feel a pinch in your shoulder blades, as if they are moving closer to one another. In reality, the majority of what you are feeling is the isotonic extensions of the posterior scapular muscles. The same movement happens when you get into the peak of the throwing motion...when your front foot is planted and you form the "half a Nazi symbol" I illustrated earlier. Your son's weak front glove side prohibits his left posterior scapular muscles from pinching to their full capability. When the body turns and the arm comes forward to throw the ball, the shoulders work in opposite motions from each other just like the upper body and the lower body do. The throwing shoulder will come forward, while the non-throwing shoulder will move just as violently backwards. By not pinching the posterior scaps fully, your son is somewhat hindering his ability to fully utilize the torque he can maximize in his shoulders.
Take this photo of Aroldis Chapman as an example:
I have my own skeptical reserves about his throwing arm action and the pressures on his elbow, but his posterior scapular loading in his lead arm is second to none in my opinion. This is probably one of the factors that allows him to throw with the velocity he does. I think that if your son was to be able to improve the strength of his glove side arm in this way, I believe that a velocity increase could potentially occur.
