Breeders tend to sell out very young pups and don’t feed with standard feeding practices. There is a good chance that the pup is younger than said. However, you can give your pup the given quantity of feed in small multiple meals. So that you may not overfeed at a time.

We can't go by breeders words some times for the age..when you got the puppy?Did you see steady growth in his weight after coming to you?..Is the puppy active?Pls Consult a  Veterinarian near by for a general check up to discuss about his Diet and weight gain etc..

Cross between two breeds always has both advantages and disadvantages. It may get any one of the parent genes dominant, or it may have mixed effects. In your case, 200 grams are low only, but to know the health, growth, and age of the puppy, it needs a vet visit. A vet can check and tell you if the puppy is really 7 weeks old or not and the health status too. As far as the food, after confirming his age and health status, you can decide the food quantity with the help of your vet itself.