Does this sound like it will lead to aggression?

Try to get him into some obedience cles. It sounds like you're doing everything half right. It's great that you're exercising him enough but now you have to give him a job to do. Get him into obedience training, then maybe look into search and rescue or tracking training...try and get the canine good citizen certificate. Maybe look into agility training. Do you or your boyfriend hunt? If so, he's a lab! Train him to duck hunt! He needs more to do but he also needs you to be his pack leader. He's a little out of control at the moment and you need to step in and be his pack leader and give him direction. When he mouths, say NO! give him a toy to chew on. Never put him in his crate as punishment. He's starting to view his crate as a negative place and you don't want that! Him doing laps sounds like a random burst of energy which he's going to have for awhile longer. Labs stay puppies until they're at least 2 years old maybe longer! Good luck! Hope I could help.