I just brought home a 28 year old YC almost 3 weeks ago. He had been with the same owner all that time, since he was a newly weaned chick. I expected it would take a long time to trust me, but it happened much sooner than I thought it would. For the first 2 days he wanted nothing to do with me. I just spent most of that time in the room where his cage is, but didn't push it. Then the third day I was outside most of the afternoon, and apparently he did miss my sitting there! When I came in, he started singing opera for me. That was the first vocalization I had gotten other than growling at me. That was a good start.
It can help if you sit on the floor beneath the cage so you are lower than he is. And just talk or sing to him. I haven't met a bird yet that doesn't appreciate a human who will sing for it. They don't care if you are a bad singer!
The other thing I did that really won him over was to imitate every noise he made, whether it was a word, a bodily function sound, opera notes, or any of his other vocalizations. That seemed to go a long way! And I praise him a lot when he strikes poses to get my attention.
I also started handing him treats through the bars. If he will take food from your hand, that is a way he is telling you he is starting to trust you. Eat in the room where his cage is and make yum yum sounds. Then go offer him a piece of your meal.
By the end of the first week he was willing to come out for me and let me hold him, and cuddle a bit.
Now some birds don't like to be petted. My Nanday doesn't. But, she still wants to come out and interact with me. She's just never going to be a cuddle bunny, but we are still great friends who have been together a long time now.