You need not be over 40, or a woman, to participate. It's about characters that are over 40 and female. For me, being primarily interested in Joss!verse fic, this covers lots of prime territory: Joyce Summers, Maggie Walsh, and Adelle DeWitt, not to mention all the vampires, gods, demons, and keys that fit the bill. That said, if a person were to write Dawn, they'd probably want to emphasize the zillion-year-old key aspect rather than the teenaged girl aspect.
They are finishing up their first set of ficathon prompts, and will go to monthly challenges starting on Nov. 1, with two "free" days each month. C'mon over! It'll be fun!
I've also been wanting to rec a little fic that keeps nudging me. It's season 6 Spuffy, it's NC-17, it's first person, and it's super short, but it packs a wallop like very few fics I've read. It's not fluffy or funny, unlike the stuff I usually rec. Plus, it's not even in the writer's first language, so it's extra infuriating that it can be so good. Hmph.
I'm talking about larabeckinsale's Look at Me. If you haven't already, check it out.