Shoulder habit

My cockatiel is with me for almost 20 days. He started getting comfortable of me at 11th day. I have a major problem with his habit, he never comes on fingers, he always runs to shoulder. If I keep him down, he runs back to my shoulder. I have no problem with that behaviour alone, the thing is, he bites after he reaches my shoulder. He bites my fingers and I have to call people to take him off. Plus he may be marking my shoulder as a territory, he is 4 months right now but after he grows up, it will be dangerous for me or anybody. What should I do? The good thing yet it that he cannot fly a lot so if I put him far away, he doesn't come. But I am still afraid of him growing up to be violent.