What will be the adult size of my american bulldog?

We've just got a 8 week old american bulldog. He weighs 3.7 kg. the vet said, who we just visited he'll be about 20kg adult size, his dad was 55kg and mum was about 30kg to 35kg. So I don't see how a pure breed male american bulldog can only be 20kg. He is a small pup as they all where in the litter, and the vets a professional so she obviously knows what she's talking about, but american bulldogs are still quite rare in England, so she may not of been aware about the adult size. So my question is do american bulldogs start as small puppy's but still grow in to a large dog?I've just worked out he's younger than we've been told. We was told on the 9th of may his eyes wernt open, but he was ment to be born on the 7th of April. Witch means he was well over a month old b4 his eyes opened, and from my experience its about 10 days when their eyes open. Maybe a bit longer but not a month.

no one can accuratly predict the adult size of your dog.If the breeder has very good knowledge of her bloodlines, she can give you a fair guess based on what she has seen in previous litters.Its very possible for the pup to end up smaller than the parents.. it depends on what genetics are in the pedigree.

Your vet is not psychic, nor am I.expect 30–58kg which would be in the breed standard

As you were already TOLD...BYBd mutts don't have a breed standard!!!*&*ALL young are small & GROW!