Honestly, by around 12-13, you're probably about ready for Chappelle's Show. It's got some language, some sexual things, but it's all in a joking matter and most of the content in his shows should be fine for most kids between 12 and 14.
I haven't seen a full episode of this show, but my friends showed me a clip about him talking about sesame street and it was hilarious. He used the f-word and it's derivitives a couple of times, and it was completely uncensored. People under the age of 16 shouldn't watch shows with language like that if it's uncensored.