Am I possibly a ?

OK, this question's a biggie. I am usually attracted to guys physically/emotionally, but I find myself extremely emotionally attracted to girls who look exactly like guys (a.k.a. butch). Obviously I know they're girls, not guys, but I have met at least two of these girls with very attractive personalities. I am not necessarily physically attracted to them yet, although I suppose that would come later. However, I would consider them "relationship material", if that makes sense. I am not attracted to all girls, just the ones who look like guys. Am I just confusing girls with guys, or is this the "beginning" of ism? Also I'm eighteen years old, wouldn't I have realized my "true" ual orientation earlier if I was ?