Hi Bella,
I hope others can help you with how to start, because others on here are more familiar with options in the US. It's possible your college club has requirements that you do or don't meet, but you'd have to ask them. And otherwise there are probably other options or clubs. You'll also need to think if you want to compete or if you prefer just training without the hassle/pressure of competition.
As for if you're to old, I would say definitely not. I started at 24, and now I'm 27 and still going. I think starting older has its own strengths and weaknesses. Strength: you understand instructions better than kids do. This helps learn faster. Weakness: you have less free time for gym practise, and it's harder to gain flexibility if you haven't worked on it while you were developing.
I see some adults learn things really fast and others have more trouble, so how much you can still learn depends a lot on you. However, no matter the speed, I see everyone progress around me. The age in our group ranges from 16 to... fifty-something? For those of us who started as adults, the skills range from "still learning to cartwheel" to saltos flight elements on bars. So it can go all kinds of ways.
If I may ask, what are your goals? Do you just want to have fun? Is there anything you'd want to learn or achieve specifically?
