Considering he will never be a great shooter, a great rebounder, taller, better jumper, I'd say the guy has come close to peaking. Back yours up please.
See, exactly my point. He's ALREADY surpassed your expectations, so, ergo, he's 'peaked.' I'm not so convinced.
He has many areas of growth. His level of fitness, for example, could be improved. He added a 15 footer in one offseason, it's not impossible for him to add a 3 point shot the next (your deft assessment of his shooting mechanics not withstanding). But perhaps the biggest thing pointing towards his non-peak is basic common sense--pro athletes don't usually peak until 27-29. Glen has at least 5 more seasons of possible development, even if it only comes from the shoulders up, it's still movement above what you classify as his 'peak.'