1. Birds that are not handled do not stay tame. He has not been handled in years. It's a pretty safe bet that this bird is no longer tame. So you need to go back to basic taming and training. Taming, touching, and step up exercises.
2. This bird had not been handled, and if anything, was mishandled, therefore he is afraid and does not trust anyone. Attention isn't enough, in order to allow you to handle him, he has to literally trust you with his life. He's not there yet.
3. This is FEAR biting. He is still afraid of you.
4. Even assuming he was tame, conures are PAIR BOND BIRDS. You are not this bird's person (yet!) You need to become the bird's person, in order for him to allow you to handle him.
Start from scratch. Do the basics. You need to start completely over with this bird.
There is nothing wrong with the bird. In the wild, you'd never get close enough to a conure to pick him up, much less touch him. Since he hasn't been handled, he is closer to his wild cousins at the moment, than a pet store bird. He can BECOME that again, with the right training... but right now he is not a tame bird.