I did some research and could only find one instance, per the SV, that specifically stated anything about the flews on a German Shepherd - and it is pretty dated - over 30 years old - so I am sure other changes have been made since this time to the GSD standard but here you go:
"Muzzle should be strong with the lips firm, clean and closing tightly without any flews."
Everything else I found about the head area basically stated that everything should be "in proportion" You can read more yourself here:
Keep in mind that as the puppy grows many of its body parts may be out of proportion for a while until it is fully mature so I would not worry too much about this in a growing puppy right now - especially if it is not causing the GSD puppy any problems.
