He coud be capped if he has very very low sublevel of potential, which is most unfortunate for you. 21y old and 213 cm, no negative elastic effect? IS shouldn't take more than two weeks to pop, so I'd say try it one more week and if IS still doesn't pop, he is capped for sure. Also if IS pops in 4th week, it could be that he is still capped, but you trained him over his potential. If he'd be my trainee, I wouldn't waste my time on him anymore. Btw, he will have around 43k salary next year.