Welcome to GC.
It's really hard to know if you're too old without knowing how old you are. Generally it would depend on the campus. I don't imagine Recruitment at CSUS is ultra competitive, but since I didn't go there I'm no authority.
Starting a new group is a huge undertaking. Why not check out what CSUS already has to offer first. There are several sororities already on campus: NPC, NPHC, Multicultural, etc. Take a look:
http://www.csus.edu/studentactivities/clubs_soro.htm
Good luck!