I coach a level 3 and 4 rhythmic team. We are a mostly for fun team but we go to 1 or two meets a year. My oldest two girls are both 13 and one is a L3 and one's a L4. The 13 year old L3 just started this year, has no gymnastics experience, but did have some dance training. She knows that she'll be the only Jr. level 3 at meets and that the rest of the girls in her level are in the 6-9 age range, but she is having fun and doesn't care. I would look for a program and go for it, rhythmic is an awsome sport and even if you don't compete it's alot of fun.
I start doing rhythmic. I know that is a little bit crazy now that I train for the "elite team" in my gym, but I want to do it. I did rhythmic when I was little but I quite because the Artistic trainings become harder and I was so much better at that sport, so I prefer doing Artistic. But now that I need less hours of train to have the level that I must have I start again with rhythmic. The three firsts weeks were horrific (I don't know if that word is ok) but know things are going better
As some people have already said it is better to start early, I am currently 14 and have been doing rg for 10 years, i guess it depends if you are starting rhythmic straight up or if you have come from another sport. A girl who used to do artistic started rhythmic and they immediatly put her up to level 5. So i guess it depends on your previous experience. Tell me how it goes!