If you are devoted to spend time with him, it would be rewarding. There's no guarantee that he will become tame, but you still might enjoy him as a pet and companion. Wait a week or so while you talk to him and try to feed him some millet by hand. Training is easiest if you have his wing feathers trimmed. Have someone who knows how trim while you help and watch. It's not hard to learn where to trim so you don't hurt him.

I found that taking him in the bathroom with the mirror covered is the easiest place to work on training.

It's possible to tame him but it might take longer than if he were a baby

It's hard but can be done read online about it

Okay so my friend has a male cockatiel, one year old and he treats him very badly. He has minimal human interaction and he is not tamed nor handfed and is really aggressive. I feel really bad for him and want to adopt him as he's giving him away. So the thing is I'll only adopt him if it is possible to tame him and make him trust me completely. But at this stage it seems impossible. Can he be tamed?

And if I adopt him, how long do I have to wait to let him out of the cage and he doesnt fly away? What is the fastest way to tame him?

I'll really be thankful for your answers.