How old are those pictures? He doesn't look 7 months old in them. He looks what we call 'wind swept' in his front legs but I would expect them to look at better by 7 months.
What country are you in? Besides barley and oats, what kind of feed do you have that is easily available to feed to him? How long have you had this colt?When sun is up he is on the free range. Would barley and oats will be a good addition to they hay to gain more weight?