OntarioSheltie
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My puppy was almost 13 weeks old when we took him home and it didn't seem to make a difference. I'd prefer to take a 12 week puppy home over an 8 week old as they may be easier to house train. Some breeders actually work with their puppies on house training so having an older puppy might be to your benefit.
We brought Sadie home when she was 9 weeks old. Our breeder had started crate training all the pups, which helped immensely. She new she wasn't supposed to potty in the crate and that outside meant potty time. All we had to do was get the timing right and watch for signs.

The only draw back to an older puppy is that you may miss out a bit on some of the cuteness of an 8 week old puppy, as they can change a lot physically in a month. But for many its a price worth paying for, if it means a better adjusted and better socialized puppy.