Help with grooming teenagers (No need for the police)

I have a lot of quality young kids at Everton in my current game (6th or 7th season I can't remember). There always are about four or five with 4 star future recommendations from the Assistant Manager who has a JPP attribute of 20, telling me they'll be as good or better than the likes of Dzeko, De Gea and Neymar etc.

But despite giving them first team football of up to 15 games (Or if they aren't up to it, loaning them out) and tutoring them with ideal (High determination etc) players they don't seem to improve to anywhere near their potential. They seem to stagnate on about a 2 star CA recommendation from the Ass Man. I've checked Genie Scout with the last two I let go out of frustration and they were at 119/182 and 121/191 CA/PA's respectively at 23 having been at the club since they were 17 or so.

Are there any guides about for this? Or any helpful threads to look in? I've tried searching but not found much. Is it something I'm doing wrong or is it fixed that some players just don't ever meet their potential?

I find that despite promising reports, maybe 2 out of 10 youngsters end up being any good by age 19. I've never checked their PA as I don't have genie scout but If they're not showing any potential by aged 19-20, just get rid of them. Also be wary of loaning them out to lower league clubs as these teams won't have the great coaches and facilities that your club has.

Another way to boost stats is to give them individual training schemes, concentrating on their strengths...Don't forget Individual Training Focus + Preferred Moves too! I find these work wonders on young 'uns