You picked a great campus! I don't really think your age or your class standing will be that big of a deal. Pledge classes at Chapman are big. The school is attracting a lot of students from out of state. I think you'll find the students there are smart, accomplished and diverse.
Recruitment may be more competitive than you are anticipating- all the chapters want to identify and recruit the best of the best. If you can get recs, do it!
You'll love living in Orange. It's got a great funky vibe. And close to the Happiest Place on Earth. What more could you want?
Good luck!