Maturity is relative. If you're younger, you don't need to be some wise village elder. Just aim not to be annoyingly childish compared to everyone else around your age. Because they're young as well, your peers won't have outgrown many of their own immature traits, and don't expect anyone to act twenty years older than they are. You can end up feeling alienated if you look down on any hint of immaturity and try to set yourself above it all.