As TM said Maddison has only just learnt how to tie his boots. But he is a great prospect and should progress to at least Championship level, injuries permitting.
We have two interesting comparisons at the moment in the club. Lamieras who has stepped down to this level, but ahead of him at the moment. Then Armstrong who is on loan and way ahead of him.
He does need to become physically stronger, especially upper body strength. I don't think "bulk up" is necessarily the right term as that would work against what makes him so good at the moment. But He does need competitive mental strength and show a determination not to be knocked off the ball or to the ground.