"maybe i am not mature enough." "-_-#, but what is mature?"

why so many girls always like to say "i am not mature enough" =(
can you tell me what is mature before you make e statement? what is "MATURE"?
it seems a big word, one of e big big words that out of my comprehension.
i only know peeple at different stages of life would have different opinions for the same things. But which is correct, the opinion she has when she was a child, or the belief she would hold when she is very old? i seriously dunno.
so what is mature?!

maybe they also dun care what mature means. it is just their method to end a conversation effectively...by talking something that i dun understand =) have a nice sleep