Alrighty then. This is my oppinion on the whole knowing your sexuality when you're in 5th grade/13. Though the two are vastly different. In todays' world, there is no age limit on self discovery. So yes, I think you can know at 13 that you're gay. I'm not saying that things don't change, but thats completely different. I won't go as far to say that you will know 100%. Because things change.