my puppy is 6month this month and she is 38.8lb is that to big for her. I talked to the breeder the other day. He called to see how every thing was going and he said that one of her litter mate a male was 46lb
slow growth is always the best type of growth. when they grow in short quick bursts your dog won't likely get as big but that slow growth makes sure bones/hips can handle the stress/weight. slow growth will usually eventually become bigger then fast, just takes longer. i rather the dog reach its full potential than rush it.
It really depends on what bloodline and if it was a tight breeding or more of an outcross. from an outcross I did years ago I got one 80lb dog who was huge and the rest normal size at about 50lbs. This litter I have now some are 46lbs and some are only 35lbs at 10 months. Your pup sounds just fine compared to his littermate.