If she is mature, she would know what kinds of people are out there and how to handle them. She would know what she wants and doesn't want in life. She should have a sense of right and wrong. A mature person would know how to handle situations of all kind and behave herself with self control. A real mature person would be someone who demands and gives respect, some one who has love, empathy, and wisdom. Be mature guys! And by that I mean, don't do anything you don't want to face the consequences of it. Only do things after careful thought and consideration. Do the right things, even if you are not popular.
-Children are no longer a "maybe" answer -If she wishes for romantic companionship, 'all' of her selection criteria pass the "40 year" test. (i. e. if it doesn't matter in 40 years, it's not valid today.) -When she can take care of other people in addition to herself. (Cook, clean, hold a job) -When her financial lifestyle is in tune with her long and short-term goals. -When it's no longer "everyone else's fault." (Mom and dad, patriarchy, past relationships, etc.) - When she is capable of an interdependent relationship and won't settle for less from another. -When she knows how to set healthy boundaries and keep them. -When she actually cares about what she can give in a relationship instead of just what she can get. -She doesn't have to be in control.
... Incidentally, this list isn't too far off from what I'd consider a mature man.