Oh boy, he is definitely claiming the room. That is the age too when they test boundaries. You have to maintain that you r the leader of the pack and it sounds like he thinks he is. My best advice is to hand feed him as long as his behavior persists. Handful at a time make him work for each handful, sit, stay etc. take your time so he knows you r in fact the boss. This has worked wonders for my mouthy Miila. If you can catch it now it will save you a world of hurt when it escalates. There are many with great experience too but this is what has helped me greatly.