Biting atiel help?

I have no suggestion to it coz' I am wondering why myself. I have mine for 1.5years and I got him when he's 3-month old. He's a very lovely bird in general and I know he loves me, anyone who played with him even the saleslady at the bird shop doing his wings and nails told me he's an extremely lovely bird. But when he's with me, like you said, I have to do what he wants and if he doesnt like it he just bite. I tried many things on him like when he bites I put him back in the cage, get out of the room and ignore him. I also tried to let him just bite but he comes back to bite more. Most of the time he shows no warning - like he's happy the last second then all of a sudden he bites. The lady at the bird shop told me that it could be because he's ually frustrated (as he's a teenager and he's the only bird at home) and so he bites the one he loves - and we just have to wait for him to get over it then he'll get better. Just dont know how long :(