I have an absolutely beautiful 1.5 yr old German shepherd female, but I'm having a hard time putting any weight on her. She is spayed, wormed and UTD on all of her shots. She is very high energy, loves to play, go for several mile long runs and aside from her weight seems to be in excellent health. I feed her blue buffalo adult dog food, around 5 cups a day, all of which she usually eats. I have taken her to the vet and he couldn't find anything wrong with her. She's a rescue and was in bad shape when I got her at 7mths she's put on about 25lb and is now around 60, and had panosteitis when she was younger. She's not grossly skinny, buts she's very narrow and people often ask me what's wrong with her and why she's so skinny?

Good food and the right amount, no illness. I am guessing she is a mix and will not take on the shepard shape you are picturing. Do her ribs show when looking straight down on her body? If not then she is likely exactly what she should be. I have several 60 lbs dogs and they get 3 cups a day so you certainly aren't shorting her on food. With this much exercise you could up her food to 2 cups 3x a day just so see if she puts on weight.

She may be a tall, narrow GSD. I've had both - the shorter, heavier dogs and the tall "skinny" kind. I've owned the breed my entire life and one dog that was underweight always, including when he died. It was just genetics.

Your dog very well may fill out when he gets older. You know he's not sick and so perhaps that's just his body type.

Depending on his height, his weight does not seem out of range to me.