Maybe it's just me, but he doesn't look all that thin to me. Not fat certainly, but hardly emaciated.

I'm glad that you've got him. Most tegu owners just don't plan properly for when they grow past hatchling stage and then they don't get enough space, heat or food. If he's way smaller than yours(at the same approx age) he's probably just stunted from not enough heat or food. Most likely, he'll catch up in a year. THat's what happened with the ill-kept blackthroat I got. I didn't think he'd ever grow, that he was stunted, but with proper heat and food, he surged in growth and is almost as big as my Moggie. I'll bet the tegu straightens right out too.