http://www.doglistener.co.uk/puppies/puppy_biting.shtml
Read through this and any other stuff you can on "puppies mouthing".
It has NOTHING to do with teething at all, so don't think this will go away purely when he gets his adult teeth. It is his way of communicating and playing with you and is totally normal. It is also no indication of aggression to come as he grows up so don't think that either.
However he does have to be trained out of it for sure.