This is pretty typical. Puppies tend to be agreeable and friendly, but as they grow older their breed personality grows more and more apparent.
My german shepherd pup at 10 weeks old would bark at strangers (people) and new dogs. He is a bit stand offish a new things, but I don't force him to socialize with anything he is unsure of. I will socialize with the thing myself, and he seems to gain confidence from watching me. I also have a 10 month old siberian husky and she absolutely loves strangers, people, dogs, or any other animal (perhaps a big too much).
One of the things I like about german shepherds is that they may be a bit standoffish at first, but they know when to stop barking. They are not very yappy for no reason.
If you are worried about your dog being a bit fearful or shy around strangers, and does not like strangers petting him, I would suggest you do not let strangers pet your dog. Your dog needs to be socialized, but socializing must be a positive experience. If your dog is forced to socialize he may start to connect strangers and negative experiences as a combo deal.
Most dogs are vocally reactive to other dogs barking, what you can do is desensitize him to the barking. Look on youtube for soundtracks of dogs growling, yapping, barking, whining and create a playlist. Play the tracks to him, and if he does not react, reward him with a treat. Use clicker training as well, it will help him realize he is on the right track.