Well, if he has good Q for now & you didn't pay a ton, not a bad lesson! Sounds like you could use him and sell him off at the season end.
Some of the slow youngsters are basically the "free" youth from levels above, they will be the "ducks". The value compared to others is the best gauge of train speed, for sure there is no exact way to tell, until you get them, but avoid the too good to be true price.