The days when you could do such a thing are gone. And here is why.
First, they ruined the tutoring system. In previous versions of FM, you could take a young player with low determination and put him to be tutored by a senior with good stats. In FM 2017 almost every tutoring action is finishing with young tutee saying that he learned just a little form the senior. Sometimes he improved his determination with 2, but nothing else is spectacular. In fact, the tutee will hate the tutor, the tutor will hate the tutee and both will hate the manager, you. The tutoring thing will succeed only if both have the same personality, which is a stupid idea. The whole point was to take a lazy youngster and through tutoring to improve not only his stats, but his personality.
Second, they ruined the training. There is an individual training based on the player's position and role selected for him. Not mentioning that I have 4.5 stars coaches for every area and "superb training facilities", focus of training is Balanced with High intensity. Despite all these, not too much improvement could be seen even after 7-8 training months and matches, even for players with a real potential to grow. More than that, suppose I train a center back as Defensive Center Back and this means he will train only marking, tackling, heading, positioning, jumping, pace and strength, then I could see some improvement in passing, first touch, technique, but none in attributes needed for his role. What's the point of this? None, you want to improve some stats, but the game says: "no, I improved other attributes". Additional Focus is a bad joke. After few months the player will complain that the training is not producing any improvement. This "additional focus" is so bad broken that if you want to improve, lets say quickness of a player, you have to select stamina or something else and maybe the pace will rise. But if you ask for quickness you'll waste your time and you will tell the game what you really want and the game will have a different opinion and you'll never receive what you want.
So forget it, take good enough players, other way you'll grow a great beard before you'll see an youngster improving in those areas where you want.