Also as Mudman said, be sure the pup gets plenty of exercise. A pooped pup is a polite pup. 
As far as the biting, IMO, everyone in the house has to be on board with no mouthing/biting being allowed. My wife and I don't like it either so that was an easy one to agree on. When the pup starts to get mouthy, have something on hand to give them to chew. Also, when biting hands, I grab the lower jaw and push the lower lips in over the lower teeth and just hold it relatively gently until the dog relaxes and doesn't want my hand in their mouth. This also provides bite feedback, the harder they bite on your hand, the more pressure on their own lips.
Sound advice here. Don't over train. A few retrieves. A few commands. Much praise. Then the kennel.
At the point a command is not being followed stop giving it. Get the pup and kennel. They will think about it.
Mostly agree with everyone above
My new lab is just about six months. Mouthing was bad but a friend suggested to let out a "Yelp" when she uses teeth. I thought it was stupid but I did it once and she immediately stopped so I kept doing it for a few days and she doesn't mouth anyone in the family after just a few days.
I was amazed it worked so I asked my friend about it and he said it's a natural thing they do with each other and they just need to know that humans are more fragile.
.02
I did the same thing. Worked well. Good add.
We yelp OW, because I figure that is the sound a kid, or adult, will make if the pup bites too hard and they are not part of our training scheme.
