It's hard to find gyms that will take gymnasts over 18, but they are out there. The gym I coach at does do beginner classes for teens, as well as beginning tumbling classes so we do have older girls in my gym just starting out.
I have a similar background as you, though I started earlier. I...
I do the AAU Ladies Division. I will actually be competing at Nationals this year for it.
It's pretty cool and you can find the rule book online at AAUgymanstics.org. It spells out the rules for the Ladies' divisions. The lowest for the adults is Intermediate Optional. The rules changed...