As big dogs said, he's close to being capped. Count the sublevels in, and he's in a dangerous territory already.
How about training him OD and passing for two more seasons, ages 24 and 25, then cap him out with another season of 1v1 forwards?
I see you have another 21y center trainee. Would this fit him as well?
You're training him for 6 seasons already, so why not 3 more? :) Don't know if you can afford to train out of position though..