Hi Mia,
He sounds like a nice bird, but he is wary of you. I think you need to have a better understanding of bird behavior and body language. Since you are unsure of him, it makes him wary of you. Cockatiels are prey animals, so they do not like to be grabbed from behind. It’s normal for him to be territorial around his cage. You need to go back to basics to work on earning his trust and then teaching him to step up. You might want to try teaching him to step up on a stick or perch. Always move slowly around him and don’t reach for him, especially from over his head or from behind. Make sure his cage is not right next to a door or entry. He needs to be able to see people as they approach his cage. It can startle a bird if someone walks into a room and their cage is right by the entry. At 6 months, he is still learning. Just be patient with him and give him time. It isn’t that he doesn’t like you, but you don’t understand him and he doesn’t understand you. I’m going to give you some links to our training and behavior pages. This information will be very helpful for you to better understand him and know how to work with him.
Teaching Your Bird
Pet Bird and Parrot Behavior
Thank you for asking Lafeber,
Brenda