My little sister is gay, but still not allowed to date?

just assure her that you are perfectly comfortable with her sexuality etc.. but as an older sister/parental figure you still have to enforce the rules set by her parents ; no dating til 16. shes still young and she'll have a tantrum and hate you for a bit but it's part of being a guardian, sometimes you just gotta be firm. (ps. shes probably just using the gay card as leverage and probably knows it has nothing to do with that. kids are crafty that way ;)