I remember in 2001 the chapter at ASU actually took a member who was 21 or 22. She was a freshman, just started college and decided to rush. She stayed involved until she got married a few years later (and then decided to go alum, although I'm pretty sure (but don't quote me) ADPi does allow a sister to be married and stay active, but I'm not 100% sure on that
). I've seen her at some alum events, so she is still somewhat active.