Its strange how much he looks likie my gelding, Stetson!
I'm just getting back into all this horse stuff (Someone correct me if I'm wrong!), but the few little things I see is that he's a bit too straight in the hind legs, he seems a little toed out in the front and back, and I think his shoulder is a bit too steep. Also, he has high withers, but since you are exercising and training him, you will probably start to see that improve. My Stetson has very high withers and I know I have a heck of a time fitting a saddle to him! They either slip back or sit right on his withers.
Your guy is very cute though! For 20 he is looking very good, even if he is a bit skinny. Looks like you have done well to get him back on track though! (Its amazing how they can look so raggedy in the winter with their long coats and so beautiful in the summer!)