No there is no minimum age at which a puppy can be parted from it's mother. Not for any puppy, whatever type of breeder it comes from. Not for commercial dealers or private sources. However, I repeat what I said before, it is not good to remove a puppy from it's mother until about 8 weeks when it is fully weaned, otherwise the pup is most likely to have problems.
Just a small point Jaybee. In your original question you used the word sold and now you have used the word parted. So I've now answered both of your questions.