Hi
Welcome to the world of gymnastics, it is an addictive one.
I can testify that 20 is not to old. I started/got involved in gymnastics at 18/19, and i over the years i have learned a few skills. However being without proper coaching progress was slow and disappointing. Good news is that a year after i start i found gymnastics coaching, and have been doing so for the last 6+ years.
Anyways in short, i would definitely work on finding a gymnastics adult class with a decent adults coach (when in the US, as many of the adult class coaches that i have meet have actually never been all to interested).
While in Cuba i would look at finding a gymnastics gym that you might be able to attend. who knows you might get lucky, and be allowed to join in on their conditioning.
I don't want to sound my own horn by any means, but check out TheGymPress.net for gymnastics articles on skills, and more. That is just one place to start to get some ideas (however there is no replacement for an actual coach). Posting on the forums is always good, go to
gymnasticsbodies.com for some great! gymnastics conditioning ideas to work strength on rings especially.
Work basics, like handstand, forward and backward rolls, cartwheels. These 4 skills pretty much make up the basics for all tumbling.
If you are getting into apparatus, than just work on swings (trying to learn the technique). With a good swing you can learn almost anything.
Flexibility work on splits in all directions, bridges, quad stretches.
Its a hard topic to cover just in one post, but some ideas