As a Polish woman I would say:
"jestem dorosłym człowkiekiem"- only when I really want to make a point of being human
"jestem dorosłą kobietą" - when my womanhood is important
"jestem dorosła" - "I am an adult"
"jestem dorosłą osobą" - I am an adult person
two last ones seem to me like ones I would use without giving attention to either my equal right as a human being, or my gender.