In my experience males tend to stay adolescent looking a long time. I don't think my mail actually looked adult adult until two.
What food are you feeding and is he intact or altered? Those both can affect their looks. Altered dogs (especially when altered young) tend to retain a puppyish/immature look throughout their lives in my opinion.
But more than likely it's because he still is a baby and you're too close to him to really see all the changes he's going through