7 1/2 heads tall, not 8 (which is why I said Marcus should be closer to 7 or 8 heads). I never told you to follow that guide exactly, and I would have given you an "average" guide if I could have found a decent one that showed age progression.
As for him being 6 heads tall, well, it's kind of hard to tell where the top of his head is, so I estimated. My bad. Either way, he still seems to be a bit on the small side to me, but if that's just the way he is, my apologies.