Your trainer will slow down the rate at which skills deteriorate for players 32 and older, other than that he is a normal L4 trainer.
As far as when to play your C at PG, you could play him during scrimmages only, but you run the risk of him fouling out or getting subbed (even if you list him at all three PG slots), I would recommend playing him as a backup for one game where you either have a favorable matchup or are clearly outmatched. Then try to fill the remaining 48 during the scrimmage.
Good luck, he is a gem of a trainee. Especially with his height and respectable OD.