Dry foods are available for puppies right from weaning age (fed soaked in water at this age) but really you should keep your puppy on whatever the breeder is feeding him for at least the first week or so. Your breeder should supply you with a detailed diet sheet and a small supply of whatever he is being fed. When he leaves the breeder for his new home, he will already be facing huge changes in his little life so it's best not to change his food too until he is more settled with you (changing food suddenly can also cause tummy upsets so is best avoided for this reason too). Once your puppy is settled with you, if you want to change the food you can do but it needs to be done gradually.