I love a rounded big man, I think I have the most rounded hybrid SF/PF in Australia.
But you really need to focus, right now, on the big man skills. For the rest of this season I suppose some passing training is ok, you may get 1 more pop out of it. Next season you really need to smash those inside skills. But I'd rather not train passing anymore for now.
I can't stress it enough. The opportunity to make the U21 side as a 20 year old has now passed. He may make it as a 21 year old, but he will be unlikely to get a start over other big men cause he may be a bit behind.
It's hard to justify starting someone who is triple sensational with passing over someone who is triple wondrous/marvelous with pitful passing.
Considering he needs work on JS as well, I'd leave passing till later.
You can always consider training secondaries if you believe his salary will get out of control and you can't retain him in your team if you keep pumping those outside skills. I'd say in Australia division III that cap is around 90k for any individual player on a good competitive team (not a one man show).