Um...

Queefing... it's pretty... uh... common in our household. Intimate moments mostly, but yeah, situps and other excercisey things, too. And we're (relatively) youngin's too, so I don't think it's really an age related thing. It happens most commonly when the PC muscles relax and allow air to get trapped, but I'm sure there are other things that can encourage it- I think also excitement that encourages the vaginal walls to 'open' (that's probably not the correct terminology, but who's really splitting hairs here?!) for me- long bike rides will do it.
*hides!*