Yes, it has been my experience by the end of the summer, they want 'out'. He never really 'turned' on us but did become a wild squirrel quite quickly. No, I never did put him in an outside cage but I'd take him outside with me when he was old enough. At one point, he climbed the tree and didn't come back down. For the first few times he'll just hang with you. Believe me, instinct will kick in. But don't let him outside or loose until you know he can crack open an acorn, as that might be his biggest food challenge outside. We always left peanuts, corn, peanut butter sandwiches, etc. out for him. At first he'd always come to eat them, then as he grew more confident and self sufficient, he'd eat our food less and less. I have also raised baby raccoons, too, and believe me, the call of the wild is still very real for them. You are just teaching him survival skills just as his mother would. He will go off on his own and that is the whole point of rehabilitating a wild animal, NOT to make it a pet, which is illegal in most states, anyway. Your goal should be teaching him to be a squirrel in the wild, which is where he belongs.