Go for it! What have you got to lose? If you don't rush, you will always wonder what "might have been" and probably regret it. If you decided it's not for you, or if that particular school's Panhellenic system is really strict on age, at least you won't wonder "what if?" for the rest of your life. Take a risk, be friendly, be yourself, and let the sisters know all the positive things about you!