AIs your dog's coat solid tan, or solid tan with maybe a black muzzle & white chest markings? If so, then he's unlikely to be pure German Shepherd. Solid tan isn't a GSD color. A genetic test could tell you with greater certainty.
His hind end looks like he's got a good dose of GSD. However, he's definitely not pure GSD with those floppy ears. I wouldn't be surprised to hear he also had Labrador, Golden Retriever, and/or some kind of hound. Nice looking boy.