The cat should be vaccinated when it is 8 weeks old and then again when it's 12 weeks old. If your cat is not vaccinated when you buy it, you shoould book a time for it! Talk with your breeder about the cat and ask if the cat has been socalized at an eairly stage.
Make sure to read this before!
The kitten should not be sold or given away until it's 12 weeks old. To buy a kitten younger than that could cause many problems! The kitten should be inspected by a vet, it should be marked with a chip and vaccinated at least 7 days before you bring it home!