Yeah, at that height, I think he'll probably thicken up a little as he matures.
In your picture, as best as I can tell (and it's still not the best angle to judge him with) he basically just looks like a young dog who hasn't quite matured yet to me. He's not as broad across the chest as some dobes are, but that may come with age.
One way or the other though, his weight looks good to me in that he isn't too skinny for his build (no hips or spine sticking out) or too fat (no rolls of fat above his tail or on his ribcage.)
He has a shiny coat and and looks healthy--
I can't see your boxer behind the photobucket seal (is that him?), but in this picture, at least, he looks a little stout?????
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And you didn't ask, but I feel like I need to point this out for the sake of your dogs, even if it is an unpleasant nag for you or something you already know......two male dogs, both of breeds that have a reputation for same-sex aggression, have a likelihood of developing aggression toward each other (and other male dogs) at some point. Even if they get along well now, and one or both are neutered, this kind of issue can show up suddenly and catastrophically.
You will need to be aware of that especially as your dobe matures. Serious aggression may crop up between the two--you may need to handle them a bit differently to keep everyone as safe as possible. Please research same-sex aggression so you know what you may face in the future and what you will need to do to live with them both in the same household.
Take a look at this thread for starters https://www.dobermantalk.com/doberma...ggression.html
While this thread gives you an idea of management techniques if your dogs end up not liking each other The Dog Geek: Crate and Rotate