I am babysitting a yorkie for a friend. He is 15 years old, still plays witht he younger dogs and weighs.......20 pounds. He is a porker. I told her she had a porkie not a yorkie.... He is so sweet and much more healthy than the female that my friend had. So, big is not always bad, not when it comes to a yorkie anyway.
You truly can't always tell the weight and size by the parents. My son had a giant schnauzer. Both parents were HUGE 110+ pounds and super tall. His on the other hand weighed about 70 pounds and was not tall at all. Not much bigger than a standard.