For me it seems inappropriate in most circumstances unless referring to someone under 18. Exceptions might include a female of the same age in a casual, friendly comment like “Let’s go, girls!” Most of the time if someone - especially a man, and especially a man younger than me - refers to me as a girl, I just get ticked off.
I find it a tad insulting and demeaning. It sometimes tends to come from guys who are insecure about a woman’s sense of self-empowerment, so I view it as a trick to try to belittle women so the men can feel like… men. If a man consistently refers to me as a girl or uses diminutive nicknames like “baby,” I will treat him like he’s a toddler.
But I’m not completely pedantic about this. In very casual situations, such as hanging out amongst friends, I don’t think about it too much. I’ll occasionally take note of who said it, but won’t mention anything about it. Come to think of it, most of my friends refer to men and women as men and women.
I once dated a guy who said that the word “man” to him sounded like “asshole.” I asked him if he wanted to be referred to as a “boy.” He decided “guy” was okay, but “boy”… not so much. So I told him that “chick” was acceptable, but “girl”… not so much.
I picked “Only if she is underage (I am female).”
When I was in my 20s and early 30s, I referred to other females my age as “chicks” (e.g., “So last night this chick at the bar…”). Now that I’m in my late 30s, though, I use “women” a lot more often. Just seems more appropriate, even though it’s still odd to think of myself as being “woman”-aged. 
My 62-year-old mother uses “gals,” but that term seems dated and (somehow) slightly sexist to me.
I like to think of you as a lady
So ‘chick’ is actually better? It always seems so objectifying to me. I’ve never heard it any any situation that did turn women into objects, but to each their own.
Marginally better, to my ears. As slang.
I agree, both are objectifying. “Girl” seems more diminishing to me. “Chick” just compares me to an adorable little fuzzy baby bird.
Okay, that’s diminishing too.
Hell, I dunno. I am woman. Hear me roar. 
Girl up to 30. 30-40 is a woman. Over 40 - lady.
I am a 23 year old female and I always used to say “girls.”
I am in graduate school for business. One of my human resources classes was the kind with a LOT of class discussion. One night we somehow got on the topic of offensive behavior at work. About one third of the class was African American women. Apparently they all found it insulting to be called “girl” when they were clearly women, citing past usage of “boy” etc used against AA people in a racist way. It made me think and now I won’t call a female “girl” unless they are a minor or I know them well enough to know they are not bothered by it.
I agree that it’s fine in most casual contexts, but can be used to be demeaning/disminishing in more professional ones. OTOH, the same sneering jerk who uses “girls” to be condesending can infuse the same nastiness into “women” or “ladies” too.
Agreed. I say “girls” in situations where I would say “guys”, but I am not using it as the word “girls” that is the counterpart to “boys.” I am using it as the counterpart to “guys.”
My two paddling crews range between 50 and 80. They refer to themselves as “girls” and as “ladies.” Sometimes I forget and I call them “guys,” but they forgive me. The flip side of the coin is that I don’t make a fuss about being included as one of the “girls” or “ladies” rather than the group of us being address as “girls” or “ladies” and Muffin.
This is how I use it.
Female, 40+ and I said other.
Among friends, we will use girls or chicks occasionally in a casual context. In a business context, it’s always men or women. Guys for a mixed group is acceptable in either situation.
It’s okay in any situation you would refer to men as “boys.” Which, for most people, means only when they’re college aged at the very outside, or else if they’re dogs. If you wouldn’t refer to a male by the term for a child, it’s inappropriate to refer to a female that way.
I voted “other”–for the most part, only when she’s underaged, but there are a few situations (that others have mentioned) where I think it’s okay (“girls and guys,” or women referring to themselves as “the girls” when men would call themselves “the boys” or “the guys”). It’s never all right for men to refer to women as “girls” in a demeaning manner. “Girls” is NOT the opposite of “men,” I don’t care how many 60s TV shows you’ve been watching.
“Chick” to me used to be offensive, but these days I’m kind of looking at it like I look at “queer” for gays–a word that the group in question has reclaimed and remade from something demeaning to something cool. Nowadays when I think of “chick” I think of “tough or independent woman.” Which is a good thing.
Thanks! I unsay all my harsh words about you, sir!
Same here. Either “girls” or “chicks” as the counterpart to “guys.” I very rarely use the term “man” in conversation to refer to a male individual, so it seems odd to me to use the word “woman” in contexts I wouldn’t use “man.” And “gal” just doesn’t quite sound right in my dialect – if I were using that word, it would be for effect. (Same with words like “broad” or “dame.”) My tendency is to default to “chick” as a counterpart to “guy” in casual conversation, unless I know the woman I’m talking to has expressed offense at the term.
I don’t really care about ages when I use it. I often use “guys” to refer to both sexes in a friendly manner when it is a group.
In a slightly more formal situation, I might use “folks.”
I’m not particularly fond of it at any time - not even for ‘girls night out’ - I would probably say something like I’m going out with the gals which looks oddly countryfied there, but it’s what I say.
It would particularly annoy me if it was a man saying it especially if he was my age. If it was a little boy or a teenager, less so. Also, if a grandpa refers to me as a young girl, I don’t object - to him I probably am.
Think for a moment why this attitude might bother people.
I’m nearly thirty. I can speak four languages. I’ve traveled and lived around the world and had countless adventures. I’m well read. I am on my way to an advanced degree. I once saved a baby’s life. I’m financially in a good spot. Sexually I’m experienced enough to be a lot of fun. I’ve had a colorful life and matured into a sharp, sophisticated, and interesting woman.
It is not a compliment to call me what I was when I was a dumb ass teenager who had done nothing. I wasn’t better back then.
The only thing that was “better” about me back that was that I was more sexually attractive to shallow men. Excuse me if “I don’t really care about the awesome stuff you’ve done with your life, what you really should be proud of is that if I squint a bit you still kind of look like an eighteen year old!” doesn’t really make me feel good about myself.
I’m not a kid (thank god.) I haven’t been one for a long time. While I love each of my wrinkles- I think of them as a beautiful physical sign of how passionately I’ve laughed, smiled, lived and loved- I am fully aware they make me less attractive to most men. I understand that I was at my most physically attractive more than a decade ago, and it’s only going to be on the decline. I really don’t need to be reminded of this. Instead of telling me it’s good that I can kind of fake being something that passed long ago, look at who I am now and what is good about that. You don’t compliment a black guy by calling him white. You don’t compliment girl by calling her a boy. And you don’t compliment a woman by calling her a girl.
In other words, don’t tell me it’s a compliment to call me something I’m not. Call me something I am- there is plenty of good stuff to choose from!