Wonder what the burn actually came from because Petco doesn't use any UTH.
Was he one of theirs or did someone drop him off with them?
He more than likely isn't "stunted", they all grow at different rates. Two of my female albinos are three years old. One is 1300g and just started pairing while the other is in the 450g range. They hatched a couple weeks apart.
There also isn't a problem with feeding live.

Post photos so we can see what you are up against.