At Boys Town, we tell them maturity is the ability to control anger, to settle differences without beating each other up. We tell them that maturity is the patience and the willingness to pass up immediate pleasure in favor of a long-term gain. We tell them maturity is perseverance, hanging in there, the ability to sweat out a project or situation in spite of opposition and discouraging setbacks. We tell them maturity is unselfishness, looking to the needs of others first and responding to them, even sometimes at the expense of our own desires. We tell them that maturity is humility.
Maturity is the ability to make a decision and stand by it, if it's the right one.
Maturity means dependability, keeping your word, coming through in a crisis. The immature are masters of alibis. The immature can't make a decision. All we are really talking about is accepting responsibility to grow up.