Maturity is more to do with the mind than with your age. Sure, your body physically matures. You cease to grow, you hit puberty. Mentally and physically women mature sooner than men, but mentally no one is mature when they turn 18.
Especially right after sending them a song like the FL/GA line song holy and calling and telling the person that is how you feel about him but could never explain. Then within 2 months in bed with someone else when he never changed how he treated you. What kind of person does that to someone????