he’s still a little underweight to move to a cooler environment. He needs to be at least 450gms – preferably a little bigger than that (600 to 800gms) – but he will put on weight very quickly in captivity. Once at a healthy weight you could try and move him to a cooler environment to try and encourage him to hibernate, but they don’t always do so in captivity – especially if a juvenile. The environment for hibernation should still include a natural light source – so garages / sheds aren’t ideal if they don’t have a window – but fine if they do. you will still need to check on him regularly in case he does wake intermittently.
fingers crossed for you and well done for getting him this far!