I got my first GSD at 16 weeks old and my second at 20 weeks old. Older puppies are fine if the breeder is doing something with them during that time. Do you know what, if any, kind of socialization the puppy has gotten? Is he housetrained, crate trained, or has he been living in a kennel outdoors? Has he had any basic OB training?
I prefer to do the training and socialization myself, but if it was a breeder I trusted, and I knew they were doing stuff with the puppy that would be okay too. We got Halo at 10 weeks old, just a couple of weeks past the usual 8, but the breeder had been taking her to training at her Schutzhund club, so she'd met tons of people, been passed around and doted on by kids, and was around lots of other dogs. If we had decided not to get her she was going to be sent home with someone else from the club for further socialization and a change of environment, which is not uncommon.