Got a cockatiel

Hello everyone. Just got a new cockatiel. Does anyone know if it's male or female? It was hissing at start and running away and biting me and screaming at the same time. But I wrapped it in shirt(like a burrito) so it can't bite me and was petting it for few minutes for days . Now it stands on my hands and let's me give it scritches(on head only ofc) and eats out of my hand, but is still a little fearful. Any advice how to tame it completely? I have a pineapple conure also but he was almost tamed already. Also is the feather pattern gonna stay the same forever or do they change their pearl patterns? It's very young cockatiel. Any advice would be appreciated! Also I'm open to name suggestions :).