SAYING that you are mature just proves that you aren't.
I don't see why if you say you are mature, you will get flamed by the community for "acting immature". Anyways, why judge people by simple phrases with no meaning like that, rather than knowledge of grammar and the "maturity" of a person's post? I know that a lot of internet communities have people who think they are the best and have huge ego complexities (R-BLOX, for instance), but you should give people a chance to prove themselves mature, whether they think they are or not.
On topic: I am 13, turning 14 quite soon, and am quite mature for my age.
I am 21 and able to live on my own(financially) however i an not mature enough to do so! nor do i think i will ever be able to handle the responsibilities of living on my own, it is too much work i will always live at home if i am allowed to!