I might be off on this, but I was told by a few folks that their eyes usually change color around 6wks old (in other words - by by baby blues and hello adult color). That might help you a bit. Are his eyes blue? Also, his weight might help a tiny bit too. I just got done with three litters myself and did a lot of research, learned a lot and was very good about weighing them. I'm by no means an expert (in fact you'll find my plea for help when I got them on this forum somewhere
Also, mine ate food at that age and no KMR because it was giving them diarreah, but to help their little teeth, in addition to the canned food, I took the dry kitten food and added a touch of warm water so that it softened it just a bit. Once they began really going to town on that I backed of the water bit by bit and now they eat the dry just fine.
He is a cutie by the way!!!