Thanks for those comments. I definitely agree. I'll take more of a look at your edit and make some adjustments :)

The abdomen feels a bit blobby and shapeless compared to the rest of the lean torso. He doesn't look bulky enough to have fat/muscle cover up his waist. I also can't tell if the abdomen is meant to be a soft belly or abs or something inbetween. The reference doesn't have distinct abs, but it looks like you're going for abs since the highlights are broken up, but your highlights are too large and too few to be abs.

Here's an edit that adds a waist and some abs (if you don't want abs, they're easy enough to soften up).
I also made a few other edits, but none of them really go anywhere. The main one is making the skirt lighting consistent with the lighting elsewhere.