This weight does seem rather small but Shepherds grow at different rates according to their line breeding. A friend of mine had a GSD pup that was tiny for ages and we thought it would never be a normal sized GSD. But suddenly when it was about 6 months old it started to shoot up and is looks a normal size.
Not all GSD`s are the same size at maturity either. My 9 year old male is over 50 kg and has been that weight from about 18 months old, but a friend's male GSD at 5 years old is only 32 kg.