Teddy was 8 months old when I brought him home from the breeder and I would do it again this way with a great breeder who is good at training. He was 100% outdoor trained and a dream.
My first, Max, was 13 weeks. I was scared enough with him at that age and size.
On a more serious note, circumstances are unique to each person and puppy. I understand why people advocate for a minimum of 12 weeks. Not everyone is equipped to care for a younger puppy, especially a delicate, tiny Yorkie.
A person who works 8+ hours a day, or an inexperienced person, I would not recommend bringing home a younger, tiny Yorkie.