On Tumblr? Since 2013.
Kinky stuff in general? I posted my first piece online in the early ‘90s. I don’t think it was that great, but a girl read it and drove six hours to let me beat her, so it had something going for it.
Non-kinky stuff? On a shelf next to my desk, I’ve got a couple hundred pages of a fantasy novel I started writing when I was eighteen. It is… not good.