Iguanas are not easy, lovey pets until you have put a lot of work into taming and socializing. That could take up to one year if you do it right and he's healthy. Less than one year if you're lucky. Even then, some iguanas refuse to give up their antagonistic posturing, tail whipping, and biting.
Baby iguanas are very skittish for many weeks. They are very stressed by their removal from their familiar surroundings and all the shipping and handling, and being put on display in a pet store. If you catch him and hold him, petting him on his head, he may hold still and close his eyes as if he is enjoying it, but he's actually scared stiff and is too young to learn that you are harmless.
Place his tank, habitat, whatever, up high where he is most comfortable.
In about 6 weeks to 2 months, when he is acclimated to his new home and the occasional appearance of your hand inside his cage, you have to start taming him. Do it by following the taming rules, and don't give up because he initially rejects you. He will bite and tail-whip, but he will be too small to hurt you. You can't put it off, because he will steadily grow and become strong enough to hurt you.
This is another source of peer-reviewed accurate iguana information, if it still comes up. My computer won't load it: