My 5 month old Gsd male kolby went to the vet yesterday. The vet said he appeared to be in good health however he was on the small side. He weighed in at 39 lbs. He was on Purina puppy but I have since switched him to authority grain free from pet smart. His sister is on royal canin gsd formula dry food and is 10 lbs ahead of him. She is taller, longer, with more muscle and denser bones. Her coat is also much softer. How long before my boy will catch up or have I stunted his growth with a low quality food?