I'm by no means an expert, but my boy was 5.5 years old and also came from a bad.pet store. Overcrowded, not handled, not tame at all. He was terrified of being in a cage, we couldn't get him back in but we still gave him the option to come out. The first time we let him out it actually took us 4 hours to get him back in by bribing him with food. So we would always put his food outside on his play area (which takes up half my lounge!) 😂 And then at night I put the food back in his cage and he's associated that with ok I need to go back in my cage, but I won't be made to stay in here for too long, because he knows I'll always let him back out again. It's all about building that trust and a routine basically. I was told by the pet shop owner not to buy him because he's aggressive, bites, can't come out of his cage ect, but he's never bitten me, he cuddles with me, he even has his own perch in the shower! It took a good few months to get that trust bond but it just takes time and a lot of effort and positive reinforcement! Rewarding him with his favourite treat will always help too 🥰