The only way to make Youth players work, without spending 'real' money, is by tanking every couple of seasons ie: deliberately not getting promoted.
That way you can train them faster than the loss of a star that happens with going up a level.
You have the benefit of building up tokens and reds/greens/blues as well during the seasons you don't go up. I use the Youth Academy all the time, tend to avoid the whole transfer market.