I'm the leader of a middle school Girl Scout troop and am curious whether I have a skewed perspective on when girls get interested in the opposite sex. I say opposite, but really mean romantic interest, so if that was for another girl, please vote as well.
I remember being shocked in 5th grade when I heard of a boy who asked a girl out. All my friends were a little shocked (and I doubt it went anywhere) and it was highly unusual. After that, I remember a friend in 6th or 7th grade who had a crush on a boy a year older and not entirely "getting" it - the drama was fun, but why did a boy matter so much? For me, I didn't get interested in thinking about boys until 8th grade.
In my Girl Scout troop, one girl has been boy crazy since 5th grade, with a significant ramp up each year since then. A neighbor has also been talking about boyfriends and dating with great interest since elementary school, and was really into boys by 6th grade. I think boy crazy is an accurate term for them. My own DD1, now in 8th grade, shows no interest. She generally thinks boys are just irritating.
I guess a related question... if you have an older daughter, does she seem to relate to boys as you did? DD1 and I seem very similar in that way, just as the mom of the girl in my troop said she and her daughter are similar. It's largely a good thing to have a daughter who is fairly similar to me - easier to predict and relate to - but it does mean I am unprepared for girls who are different, so I thought a poll here would let me see a broader perspective.
eta: I hit puberty early, and my 8th grader looks almost fully grown. No waifs or late bloomers here, so I am not sure if physical puberty matters that much compared to personality.