I saw your photos and he looks pretty healthy to me but you're right that he doesn't look a year old. His body isn't filled out yet and he still has quite a bit of growing to do. His arms will probably bulk up a bit more. He is likely just a late grower and has some growth spurts left. They don't usually stop growing completely until 18-24 months although a lot of them are full size before then. It really depends.
As far as food goes, I would still offer 1 bug meal per day all he wants in a 10 minute or so window. Make a salad for him every day with 2-3 items from this list
http://www.beautifuldragons.com/Nutrition.html and rotate depending on what looks fresh at the store and what he seems to like most. I would keep this routine up for a while and see if it helps him grow a bit. Keep track of his weight so you can chart it out to make sure he is still increasing in weight.
Lighting is also quite important for their digestion, growth, and overall health. What are the surface temps around your tank? What do you have for a
UVB light and how far is it above his basking area?