If you're single position training he might be able to make it, he's starting out with good inside skills and nice secondaries. Big men also tend to have form issues on the U21, so if you have good minute management that increases his odds of seeing playing time. The problem is that even if he doesn't hit the cap before he's 21, which he probably would, he definitely will during the season he makes the U21. So, even if he did manage to make it initially, he probably wouldn't stay for long.
There is also the issue of salary. A U21 center is so expensive in terms of salary that even if you do manage to train him high enough, you'll likely have to sell him that season for financial reasons.
If I were you, I would train him for a season or two, then sell him while still trainable to maximize your profits, or just train him to fit your team's needs, which would mean more outside skills and less inside ones. With some one on one and passing training in addition to the typical inside regimen he would be a very dominant PF for you for many seasons, and much more effective for the salary.