From 0 to 8 weeks puppies learn good dog behaviour from their mother and siblings. A pecking order is developed and they learn that they cannot bite or attack without consequences.
They learn alot from play with their siblings. Pups that are rehomed too early have alot of the time behaviour problems.
Sleeping Border Collie Puppies
Behaviour problems such as been very shy nervous and afraid of everything, others will be biting everyone and overly hyper. Breeders who want to rehome their pups before 8 weeks are usually just looking to make a quick buck and don't care about the pups future.
This critical time when the pup learns bite inhibition,how to act with other dogs cannot be got back. Orphan puppies should also be kept with their siblings they may not have their mother but they can learn from each other and other adult dogs.
If a puppy is taken from their mother and littermates before 8 weeks it will be more difficult to train.
Very young pups are also alot of work. At 12 weeks there is less puppy destruction they have more manners and are housetrained to a degree.
At 12 weeks you are better able to judge the temperament of the puppy and its general health. You do not want to bring a sickly puppy into your life and go through the trauma of it dying. Many horrible breeders still sell puppies knowing that they are terribly ill.
It is also better to have some age on a pup when you are considering using the pup for work.
The older the pup is the more interest it will have in working sheep if that is the way she/he is inclined. It will save you from having a working dog that is not interested in working.