Hi and welcome to yorkie talk! I know I am going to get yelled at for this advice, but it worked! My yorkie, who is the love of my life, is 3 now and never bites anymore. She did the same as a pup and actually was a little vicious, it wasn't always playing. I did get her at 2 months old. I was afraid to let kids pet her, as they always want to do, because she would nip at them. A trainer told me to take a rolled up newspaper and everytime she nips - wack her (she said anywhere, but I wacked her on her bottom) - she said never use your hand, always the newspaper roll. I hated doing this, but you know what? It worked! It worked after about 4 times. Then all I had to do is show her the newspaper during a growl and she would calm down. She knew very quickly that was bad behavior. The trainer said you have to stop the biting early or it can be a very bad habit not to mention dangerous. Bailey doesn't nip people anymore (but she saves her agression for other dogs - afterall at 4 lbs. she feels she is the alpha dog!) Good luck.
