Would you ask one of your sister friends out on a date?

[China]

You should definetely talk to your sister first out of respect.

There is a lot to think about. I personally have had my reservations about dating my brothers friends. When you and your new girlfriend get intimate, there is a good chance she may tell your sister about the experience or a mutual friend, who will end up telling your sister.
Its possible that she may run to your sister for advise during arguements and disagreements. If things end badly, it could end the friendship your sister has with her.

I think life is short. I don't want you spending the rest of your life thinking what if she was the one. I'd go for it. Your sister is going to love you, even if things go sour. I think if you decide to pursue a relationship, set up some bounderies.