So my Toby is now 5 months and he is 8lbs!

I am starting to wonder if he really is a purebreed.. I've seen yorkies that are 4,5lbs fully grown and Toby is getting bigger and bigger and he is only 5 months old! Here are some pictures of him, what do you guys think? His ears don't stand up either...When we bought him the people gave us papers but I doubt he is AKC yorkie..he just don't look quite like a purebreed yorkie
[img=http://img36.imageshack.us/img36/9236/dsc02074n.th.jpg] http://img36.imageshack.us/img36/8000/dsc02229d.jpg