No worries, he really has alot more growing to do physically. I have heard several breeders on the board say GSD are done growing at 2-3 years of age.
My intact male just turned two. Height wise it seemed like he stopped growing around 14 months, he's been a consistent 25", he's 72 pounds currently, I really don't see him going over 75 pounds. He has filled out more over the last 6 months, but not gained weight if that makes sense.