Guys and ?

I've decided that someone needs to take on the task of inventing a new word. Not just any word, I've got one in mind:

There's no acceptable female equivalent for "guy" in the English language.

I, personally, constantly use the term "girl" to refer to females my age or around my age, but really that's the equivalent to "boy".

I rarely use the word "woman" because it just sounds so stuffy and mature. It's not natural for me to say that I was talking to this "woman" the other day when she was in her twenties.

And I refuse to believe that "gal" is an adequate term unless you live in the South and square dance on a regular basis.

"Lady" just makes me think of Lady and the Tramp, or some women at an English tea party.

"Chick" is acceptable in certain circumstances, but isn't really a word that a female can use to refer to another female. That's a word that should exist primarily in the male vocabulary.

So, someone please invent a new word for me to use. Thank you.