I was several times in a similar situation, because I usually start the game with a lower league team and have problems with transfer money and with attracting good coaches. So, it's sometimes like second or even third season when I have the possibility to bring in such young talents. And even if I manage to bring some of them from the first season, I still have bad coaches, but at least I can play the youngsters straight away, because of the lower level of competition. You can see the difference in training and in value increase when you play them regularly in the first team (like in 10 competitive matches you already can see their improvements). Of course, you need a good training schedule as well and an appropriate tactic. Also, when starting with a lower team, you need at least 2-3 seasons to reach the first division in the country, so it takes time. Depends on luck also, for example I bought once J. Helan with like 100k and played him as first team and he never got it going, so I had to sold him in the end (was unsettled, unhappy and bad in training). Another example: I bought once Nsue with the same price, like 100k, and after 2 seasons he was scoring like **** and had value 7 millions, with big teams offering around 15 millions for him. Anyways, you have to make sure you have the best coaches for your level, to play the youngsters in first team, to loan them to teams that play them in first team, to put them to learn from your club best players/icons and so on. The rest, is just luck or bad luck (like I had once, in first season, for example, Shelvey inured twice for a long term, like 6 months totally, with long periods when he was not training at all and, obviously, not playing either).
Good luck with your players mate, cheers!