I think let him take his time and learn the ropes. It's better that he becomes confident in his skills and keeps playing beginner for a little while, rather than being forced into intermediate or even normals while still struggling. It's going to test your patience, but watching him improve will be worth it.
I tried to teach a cousin a few months ago. She was struggling pretty hard, and I even asked a few of my friends to help. Now, she's doing better after having a lot of time to improve. So he probably just needs time to practice.
Also, he doesn't have a keystone yet. That could help, even though there's still quite a few levels to go.