I discovered by accident that I was kinky almost exactly 3 years ago, two weeks after my 40th birthday. I'd connected to the bondage.com IRC server to chat with a friend of mine, and after chatting with some people I thought, oh, yeah, this is right.
Ever since then I've been looking around within the arena of diverse sexuality to find stuff I was into, so I don't know if any discoveries I made after that count as accidental. Now I know I'm a bisexual polyamorous kinky top. I do remember that the first time I picked up a flogger, it felt perfectly right and natural and I was able to throw it accurately almost from my first swing.
One thing which turns me on the most is when a person I like is so eager and willing to do things for me which they don't like that much, just because I want them to. Owning their pleasure is a big part of motivating them, and their desires and pleasure turns me on too, so I am less interested in any one specific fetish, and more interested in how they tick - if that makes any sense.
Having said that, I think I always knew that I kink hard for yummy food to eat, especially sushi, and that remains the same no matter who my partners are. So that was more an "always knew" thing rather than a "accidental discovery" thing.
I kind of feel like I was cheated out of all those years of enjoying my flavour of sexual diversity, because of being misled into thinking that vanilla coupledom was all there was to relationships. Still, I know now, and I'm making up for lost time. :)