he is still training fast enough, so surely you shouldn't sell him at this point.
If i were you he would stay probably until his 29-31, so i would train him in that persepctive. Therefore i would train cross balls, balcontrol and passing. I would train PI later on when the other skills have dropped in trainingsspeed.
If you train him to make huge profit when he is 22, then train PI, cross balls and Balcontrol.