I would regulate his food. Two cups a day, 1 cup ea. morning and 1 cup at night until about 25-30 lbs then 2.5 cups. I feed my puppy Pro Plan and feed her about that much. She weighs about 32lbs or so. I can't see her ribs mainly because of hercoat but I can feel them. The vet told me she's the perfect weight. Anyhow, you should just be able to see a hint of ribs and backbone.

From what I understand (which isn't much) from Doc E, Protein + Fat = rate of growth. The less Protein and Fat the slower the growth.