How old do you have to be to help out with set design, backstage, costume, makeup, ect..?

I agree, call them or check the website, i also know they have students volunteer as well, or they have in the past...but yea check it out and post what you find..

Call them directly

I'd call the theater for information more tailored to your needs. I'm not sure if you mean "help" as in be hired or volunteer. I do know the backstage staff are professional theatre's guild members. The website also has a lot of great information. Good luck!