How many T you gave ? 12 ?
Well, at least in cardio had good gaining. Maybe try this one training and if he is good to that, maybe he can gather some extra sp.
But yes, the practice is bad - if you consider that he is more a 3* player (65q) than 4*.
Unfortunately the gaining is not increase by the time - only in next lv when the player looses a star.
So, you can have him as back-up GK, give him any sp he can gain, training him often in two bars but not giving him extra boosters and sell him.

i signed a 24 token youth and he was worse than stats posted
My faster trainer so far was an academy player 21T but youths are a bit of random.
While an expensive nordgen has a standard pattern in training and I never had a failure, academy players don't.