From what I can see about age 6/7 and not much higher than that. It looks like they pretty much have a type and an age for those lower levels. I haven't see much on the higher levels and I'm terrible at guessing ages.
My DD had tryouts at 2 gyms in DFW for Level 3 and I'm not sure how to evaluate the differences. One is Kurt Thomas and one is WOGA. I've considered adding Metroplex but we didn't have a good experience with them at the preschool level several years ago even though people rave about that gym...