I've always been told if you can feel their ribs when you gently wrap your hands around them, they are not overweight. If you can't feel the ribs, definitely overweight.
Perhaps cut down on the treats, and try to find a quality dry food that he will eat regularly. He's still young, so I don't think I'd put him on a strict feeding schedule, but I know other's recommend a feeding schedule rather than "free feeding".
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