This started about 6 mths? Beginning of butt head stage - up your training. If you aren't with a trainer now, locate a good one. You have a lot of his basics, but that extra set of eyes can see what you and the pup are doing and get you headed in the right direction. Keep in mind for some dogs, the down position is a tough one as it can be seen as a vulnerable position.
The staring and licking may be from boredom and/or the beginning of OCD behavior. Up his exercise and again his training.
Your pup isn't mentally retarded as you put it, but he does need a good vet check that includes a discussion of the 2 behaviors of staring and licking. Then a good training program with a trainer making him work his brain and body.