Worker,
I shared your same presumption initially. However, the phrase, "I want to be the best around in the 3200 in the spring. I ran 11:02 in the 8th grade" made it questionable enough for me to inquire.
On the one hand, 11:02 off of 10m seems like a guy. However, such an individual would be extremely naive to be thinking that he could be the best around without a huge change in work ethic/attitude. Maybe, his definition of around is something akin to around the block, or in the whole neighborhood.
If, we are talking to girl, then, you are right, there are not many. But, clearly, she would have a legitmate shot at "be(ing) the best around" by next Spring. In this case, she could have been one of those people that counts miles funny... like only the quality miles.
In my opinion, either scenario is unlikely, but possible. Since, the girl would be put in a better light, I choose to believe that this person is a girl until I hear otherwise.