I don't know very much about adult dating, mostly because I'm not an adult. But I do believe that when you want to start a relationship with someone, be sure to start it honestly by getting things straight. You guys don't want to go off on the wrong foot so make sure that all the basics are cleared out (like name, age, occupation, etc.). So yes, I do believe that you should tell her your age. If she doesn't like you because of it, then that was rather shallow of her (but somewhat understandable) and there will always be someone else.