I don't think that age is very accurate at all. I don't even let my puppies go until they are 12 weeks (3 months) old. Most (not all) Yorkie reputable breeders won't, so how would the pups be trained to do all that by then? From my research and experience I believe that they are still socializing at 3 months and it is a great time to introduce them to training.
IMO-I wouldn't worry about it too much at this age...but I think it's great that you are working on it though. And I think it's great you want to have him obedience trained and you are doing it
... and he sits already, way to go!!!
