A girl is a little kid (5-11 yrs old). Doesn't necessarily have to just be age. Some older females act like girls (immature, temper tantrums, irresponsible/ doesn't take any responsibility, depends on other people for money, attention, etc.).
A young lady (preteen-29 yrs old) is an emerging woman that learns to be more responsible, pro-active, etc. Even so, still got a lot of growing up to do; constantly make stupid mistakes (bad boyfriends/friends, staying up all night/get drunk when they know they got work in the morning, spending $500 on shoes with their credit card when they don't have a job). Depends on friends, parents, not that independent emotionally or physically. Naive and haven't found themselves yet
A woman (30+- death) is much more mature, responsible and productive. Has healthier relationships and knows how to balance things. Work with people, not combative, don't make stupid ill inform decisions. Knows herself, more confident, accepts flaws. Has a lot of experiences (which makes them more mature).
That's my opinion (P.S. just because you are certain age doesn't mean you have to be in those categories I mentioned. IF you're 28 and consider yourself a woman!!!! GREAT!!!)