We got Yoda at four weeks. He comes from a champion lineage show dog, but this family only breeds now and sells Yorkies as pets. I honestly think Yoda bonded so much with us because he was with us since he was so young. The first few days he was terrified, but we were loving and caring. He slept an awful lot (maybe 18-20 hours a day) the first week or two we had him. It still took a while to train him, but he hasn't gone bathroom anywhere he's not supposed to. He does occassionally throw up, but we don't get mad at him for that.
I don't know why either, but most places recommend at least 2 months before they will let you take a Yorkie. Perhaps they are looking to show their dogs, or see if any of them are of the smaller variety, as the smaller ones can command a higher price.
I'd suggest going to the breeder in person if possible, and discussing or looking at the what kind of breeder they are. But, if they are adamant about not letting you take a Yorkie before 12 weeks, there's really not much you can do.
