"Kevin's an outstanding player who definitely become more mature as he goes on," Caldwell told the Lancashire Telegraph.
"But it's about becoming more mature day in day out, more and more.
"He's come from a club, and no disrespect to Dundee, who are not at the top end of Scottish football, so he's had a lot to learn since he's come here.
"But his natural talent is as good as anybody I've ever seen and I'm including a lot of big players that I've played with at Newcastle. He's phenomenal.
"I would just like to see him move on and just get up to that next level.
"When he does, there's no question he's going to be a top, top player for a long, long time."