nate,
you sound like you've got your head screwed on pretty good for a kid your age. i'm about twice your age now, but not too old to remember what it was like, trust me.
anyway, you are well on your way.
when does that magical day come? it's a progression. i wish i had half the sense you just expressed when i was your age.
true maturity is doing all those things you just talked about, but really feeling them confidently deep down in your soul, you know what i'm sayin?
true maturity is not giving a fuck what other people think.
true maturity is realizing that you don't know shit and you never will.
but still doing your best to be a positive force for yourself and those around you.
most importantly, i would say that true maturity comes when you realize that the answers to all those questions which you seek will likely never be realized, but you still come to peace with it and love yourself and those around you the best you can.
those questions:
what is the meaning of life?
how long will i live?
can you ever truly trust another person?
etc etc
they never get answered, you've got to exist in spite of them.
hope this gave you some wisdom.
EDIT
oh yeah, one other thing: true maturity comes when you realize that we are all always alone. you are alone when you're born, alone when you die, and we are all alone in between. we may be "around" other people, but we are always truly alone. you never really know what is in the head of other people, so you never truly know them, and vice versa. hence being ... truly alone.