Make sure they know you are a first-year student!
Give them a (short) explanation of Running Start - just tell them that you had the opportunity to take college classes when you were in high school, but you are (this is most important) scheduled to graduate in 3 - 4 years.
If you explain, you will stand out for your grades/smarts, not your age. I'm sure they will have your class standing (fr, so, jr, sr), so be sure to do this. It is a lot harder to go through formal recruitment as an upperclasswoman.
Don't worry too much about Running Start (or veganism - I agree with Phoenix, it shouldn't be an issue) - every sorority wants to have a great GPA, and you sound very smart!
Good luck!