You can try a gray forum but you will find that the larger birdsites end up been more confusing than helpful because of the large number of answers, most of them contradictory.
If the bird has yellow eyes, he is not 8 months old, he is a full adult bird and, as such, impossible to calculate his age. The fact that he is an adult, added to the things you have told us (his fear, the growling, etc) leads me to believe that the bird was poached from the wild (which is what you commonly find in Africa and Asia) and not captive-bred and hand-fed. Just as information, baby birds bred in captivity are hand-fed to make them imprint to humans which makes them believe that humans are part of their family while wild-caught birds don't trust humans at all.
I suggest that you stop offering food in your hand for now and just keep him company for hours and hours and hours every day following the 'approach only as near as the bird will allow without reacting in any way'. This will help him begin to start accepting your presence without your asking for anything which will, in time, create trust (you should talk, sing, whistle and, if he doesn't get scared or moves away from your hand, offer him a treat every now and then). Once you see that the bird no longer reacts negatively to your presence near him, you can start letting him out of his cage for flying and, once he doesn't fly away from you and eagerly approaches you for a treat (it should always be the high value item!), you can start target training. But this won't happen any time soon because, if I am right and he is an adult wild-caught, it's going to take a loooooong time for him to trust you...





