I'll be honest and say I started RP'ing at about 9/10 (I'm 20 now), and it was awesome. Granted, I was very lucky lucky and always found patient and kind players and I ended up learning a lot. And looking back now, it's not a big deal. And RPing with younger people now isn't a big deal to me.

That said, when you start that young, everyone is going to be older than you. So keep this in mind if you're a pre-teen or young teen; more often than not, the other players will know better so don't be rude or quick to anger. Also keep in mind your characters will often be older than you--ask what it's like to be at this age or that age. Ask questions when you don't understand. And stay OUT of 18+ RPs. ALWAYS read the rules before going in and ask if the age level isn't listed. Personally, I would also advise avoiding one-on-ones unless you know your partner very well.

Stay safe, don't do anything you're uncomfortable with, and save all your characters so you can laugh at them when you actually learn to make better characters.