If you wish to submit prompts (or join/watch the Comm) and remember you don't have to be a writer to submit, you can do so by going here.
We've had a nice selection already covering thirteen fandoms and various pairings, plus prompts that are non-specific to a pairing within the given fandom, but the more the merrier.
The prompts can be:
And you can mix and match when submitting, or just submit one type.
Also just to remind you (yes, again) the characters only have to be 40+ in the story, not in canon. (Of course they can be 40+ in canon as well, but that isn't part of the 'rules').