Yep, you definitely got a big boy there. I’d guess that his strength and coordination have yet to catch up with his frame. That will come in time. But, be aware that these defficiencies will limit what he is able to do so you need to set your expectations accordingly (I’m not implying that you haven’t).
That said, I would focus on a few basic things that will form a solid foundation to build on.
First, I would minimize head movement. He tilts his head to the side and such a posture change can affect performance and health. Get him to keep his head upright and to take his head straight to the target. I’ve told my pitchers to imagine their heads being bowling balls rolling down the gutter - they only go in one direction.
Next, I would focus on his glove. He drops the glove and that can also affect performance and health. As he strides and extends the glove out front, get him to keep it out there. As the shoulders rotate, the glove elbow will drop and the glove will turn over. But it should stay out front and the chest should move to the glove. Stabilizing the glove out front will help his consistency and it will enhance his timing for when he is better able to perform more advanced mechanics down the road.
He does need a higher knee lift, more momentum and a longer stride. But he may not have the core strength right now to stabilize his posture while doing these things. So I would work on the items I described above first and then start to work on these.