I am a male, and play as male characters. If I'm setting the stage, I might introduce background characters which can be of either gender, of course, but my primary characters are male.
Anywhere from about 21 through late 30s. I'm 31 years old myself.
I'm dominant. It varies in the degrees but I tend to play as a character with a position of power, or at least greater sexual experience. I can do fairly vanilla circumstances, but my characters will still serve as the seducer/corrupter.
White. It's easiest for me to play white to avoid acting culturally insensitive.
Personally I'm average height and average build. My characters tend to be a bit taller than me, but similar in appearance-short hair with angular faces. I don't do short guys well.
I like to play in different kinds of settings. I like futuristic settings, though I don't always like established universes because it feels awkward trying to squeeze my actions into the canon (for example, a Star Trek or Star Wars RP). I enjoy the relative freedom that comes out of taking inspiration out of established works, but ultimately results in my own world-building. A talented co-writer can help me to craft a rich universe that fits what the story needs, and it also leaves the freedom to pull anything out of my ass if I really need it
. I also like fantasy settings in Tolkien-esque fantasy worlds, or in George R.R. Martin-style grim and gritty settings.
I have a lot more of these than I used to realize. I like dominance and control. There's a lot of things that complement that which excite me. In my darkest moods: Sadism, Non-consent/rape, slave, training, humiliation, public humiliation, forced orgasms, bondage, mind-fucking, programming. I don't necessarily need these elements, but they're examples of things that might come up. Spanking/whipping is something that comes up, but one of the most common is simply restraining my partner so she can't easily get away, either through pinning her down or tying her up.
Most things involving food, actually. Pain for the sake of pain-if it's part of punishment or humiliation, or if my partner is a true masochist who gets off on it, that works. But the biggest thing is poor communication or unresponsiveness. Sometimes writing intensive scenes that require a lot of set-up and put my partner through the wringer can really result in the mood being ruined if it results in a two-line response. It ruins it for me like nothing else.
Also, anal sex doesn't really appeal to me. Though I can be talked into it if my partner wants that.
Underage role play, scat, watersports (basically anything that involves the toilet), excessive gore, mutilation. That's a solid start, though there's a few more too gruesome to even think about.