I think how much they bark can depend a lot on their personalities and what they have been exposed to. If they hear other dogs bark they tend to pick up the behavior pretty quickly.
Gracie barked when she was about 4 or 5 months old. She had a litter of kittens that she used to herd around when she was a puppy. She would get all excited about playing with them and would bark at them now and then. She still does on occasion. If one of the cats gets near one of her favorite toys they will hear about it!
