you can know for sure when your in your older teen years, like eighteen or nineteen.
maybe fifteen or something.
if you're twelve or thirteen, it's all purely in what you decide. go with what you feel.
if you feel your gay and could see your self with another man, the you might be.
in the teen years (as many have said before me) hormones are raging and you might be asking yourself if you're gay for a while.