It would be in your best interest to stop thinking about their astrological sign and just deal with the person. You're trying to put someone in a box according to their birth date. Not all Gemini's act the same, feel the same, look the same.
So if you're interested in someone, just get to know them, see if you're a good match, if you have anything in common. You're also limiting yourself as you frantically try and find out their sign to see if they are "worthy" of your time. Find out what sparks your imagination in a guy, what characteristics you feel are important, do they share your values, etc. That's how you know you've got a good match.