How much should my Giant Schnauzer weigh at 12 months?

My vet told me to put my 12 month old Giant Schnauzer on adult dog food because he is already 80 lbs. Is this normal?
I thought giant breeds weren't fully developed into "adult" dogs until they are 2 or 3 years old?
I don't want my 12 month old to be undernourished because he's not on puppy food anymore.