Castro moved quickly through the Cubs' system this year and is playing well in the Arizona Fall League so far. The 19-year old could make the Cubs' roster with a good spring training. "I haven't had a player go through the system who has done what he's done," said Cubs player development director Oneri Fleita. "He's certainly surpassed any expectations we've had. It seems like it takes some guys a year before we see any gains. We're seeing gains in Castro weekly, monthly, if not daily. Who knows?"