I promise this puppy is not being aggressive. It may be excited, playful, and maybe a little frustrated, but puppies are not "aggressive" - the tricks I have used in the past is to put a treat between your fingers snugly so the pup can't snatch it out. When it bites, yelp like an injured pup (high pitched, short YELP) and take your hand away. Try again, repeat as often as necessary. Once the mouth is soft around your fingers, give it the cookie. Repeat x a million. I used to feed Sadie's entire kibble meal this way, one piece of kibble at a time. She loved her food so she was very eager to alter her mouth to get food faster. Good luck.