Well, that the potential is there, anyway. I'd still say it's pretty unusual. But yeah, without sufficient food, you won't get the chance to get that tall at all!
Lol, well, of course he didn't eat enough to get that fat. Those Sumo wrestlers do that on purpose. And, who knows if maybe even there weren't exercise regimens for the wealthy at the time. Actually, they probably weren't. I'd imagine servants did everything for them. In any case, Kagawaki was a tall, fit man. Lol, how funny would it have been if he was fat, and Naraku was a fat guy the whole rest of the series.
Now that I think about it, not only do we never see Onigumo's face, but Naraku doesn't really have a face of his own. We tend to think that was his face, but it was really just Kagawaki's form that he took and decided to keep.
I'm not sure how you even know how old Kagawaki is, but I suppose that would play into things. People always used to say that Inuyasha was a little older than Kagome, like 17, and there were even threads saying he could get in trouble, because of age of consent, and such. Though, you've been saying he's effectively fifteen, but I'm not sure it's ever been stated anywhere. I think someone said Inu was 17 along with everyone else's offical-sounding ages, that were correct, so I took his as that being right too, I guess. But, we've been over this before, already, I think.
Also, that's pretty weird. I just checked that thread where someone asked why Kikyo and Kagome don't look the same, and you said almost the same thing I just said here. That it has a lot more to do with their expressions! Man, I really want to hunt for one of Kagome's serious/mad/etc expressions, now. I bet she would look just like Kikyo, then!