Girlfriend is a twin

If you're talking about a birthday gift, maybe. Otherwise, no. You do not want your own girlfriend to start wondering what's going on, do you?

I'm a twin. I never expected or imagined that my brother's girlfriend would give me a present on our birthday nor did I ever feel it would be necessary for my girlfriends to give him a present.

But I think that if you gave her a card or some such, that would be fine. It never happened to me that I can recall but I wouldn't have been bothered by that.

No, I think there is not a single girl exist on this planet who wants that her boyfriend give a gift to another girl.

Hahaha! Gifting people make them happy, you can buy gifts for her too.

Only if you are close with her as well - otherwise it should be no different than if your girlfriend had a sister that was not a twin. Would you give that sister a gift?