Samson is 8 months old and weighs 4.8 lbs. He looks a little thin (he's long too) but the vet said he is still a puppy and probably burns off all of the food he eats. (he eats a good amount everyday) The vet said he is fine. I'm guessing maybe be will fill out a little as he gets older. I think as long as your baby is eating and playing like a normal pup he's fine.