He looks just like my old guy did when I got him. But after about 6-8 months he was beautiful. Take pictures of him when you first get him home, then give him a good worming and get him on some groceries (be careful not to overfeed) then take pictures once a month. If you don't take the pictures you forget how far they have come. Because I was looking at him everyday, I got discouraged thinking he wasn't getting anywhere. My husband (bless him) would have me get the pictures out and look at the progress over the months.
My old guy is now 25-29 (not sure)and he has arithithis and can't keep any weight on. But he's the first one to greet me at the gate and the last one to leave me. His looks are gone but he's still beautiful to me.
Good luck with your guy.
PS. I would have his teeth checked soon as you can.