You know, I'm (almost) 24, and I am an alumna. I went back to my chapter for Pref last semester, and while it was beautiful, and I know a lot of the graduating seniors, I can't see myself fitting in with the PMN. These girls are 18 and 19! I have nothing in common with them. I am still in school (law school) so its not like I am in the working world (perhaps its a different story when you are a 25 year old undergraduate)... but I can see why the women wouldn't want to give a bid to an older girl. They're afraid you might drop because you may not have anyting in common with your pledge class. You're older than the seniors! I wouldn't take it personally AT ALL.
im not trying to make you feel bad, but I am around your age and I really think there is a big difference between our age and freshmen/sophomores. They can't drink legally!
have you thought about AI?