I suppose it all comes down to how one defines being mature.
I didn't fully believe I was mature until after I moved 2000 miles away from parents, got a job, my own apartment, and built lasting friendships. I believe there is a strong link between being independent/self-reliant, responsible, and maturity. I was 21.
I've known a lot of girls/women who were extremely naïve and gullible, they go to the bathroom in packs, overstep boundaries in their friendships, believe that getting pregnant will keep a man bonded with them, develop insecurity complexes and body images based upon models on the covers of magazines, or form clicks and put down other women. Need a man to feel validated.
I believe most people attribute maturity of women over men in relation to their bodies starting to have periods, reaching their full height, and having the desire to get married/settle down at an earlier age than men desire.
However I personally do not believe that one's physiology is an indication of their "maturity" nor does wanting to get married and have children.
My definition of maturity is someone who takes into account the potential consequences of their actions (before) they do anything. He/she is empathetic of others, confident in themselves, knows when it's appropriate to "cut loose" and when to display the proper decorum based upon circumstances. A mature person thinks for them self and does not rely on their peers to "validate" them or make important decisions regarding their life.
They can be trusted because they've handled issues responsibly.