I'm more used to NFL Combine measurements, but in that realm I don't think I've ever seen a skill-position player (somebody who touches the ball) below a 26" vert. In that context, 30" and below is generally pretty bad, 32-34" or so is more-or-less average, 36"+ is very good, and 40"+ is rare/outstanding. At the NFL Combine this year there were only 6 players who tested at/below a 24" vert, and all of them were 288+ pound linemen.

Obviously NFL and NBA test vert a bit differently and have different requirements with it, but there is no sugarcoating a 24" vert. Just hopefully that's something that he can improve a bit with a proper strength and conditioning program.