I hate kids who try to act really mature, and as soon as they turn 13 every time someone calls them a kid they deny it and say 'HEY, I'm a teenager now! SO shut up!' By doing that they're proving their immaturity.
If you're a kid, enjoy life, that's what I do, but don't be a douche and try to be brainwashed by adults. Being mature at a young age is overrated, and as far as I'm concerned, you aren't a real teenager until your 15 or 16, no matter what the numbers say.