age limit on rushing?

Hey! I'm asking for a cousin of mine, she's a little older (mid twenties) and she and I were talking the other day of joining/rushing a sorority and she brought up that she thought she wouldn't be able to rush or join because she's too old. She's put off college for some years so she could save up the money. And her question got me thinking as well! Is there a specific age range you have to be in order to join or can you really be any age as long as you're in your first year of college?