I came to it later in life, and lord do I regret waiting that long!
I watched a lot of porn, and more often than not identified with the woman in the video. I know most of the noises she made was acting, but damn, she plays it up that it feels good! I wanted to know how it felt, and without a pussy I had to try the third most used hole (third most used in straight porn that is!).
I started with a finger in the shower. I am a runner, and coupled with never having had anything inserted into my ass I am very tight. It took some soap to lube my finger enough to slide it in. I imagined the guy sliding in would feel how tight that I am and it would excite him more, and the thought of pleasing him made the sensation all the more pleasurable for me. I finger-fucked myself, enjoying the sensations and imagining how my tight ass would make him feel. To this day I get a lot of pleasure knowing I am pleasing him, and luckily we tend to feed off each other, the more I please him, the more he pleases me, etc.
It wasn't long after a few finger-fucks in the shower that I bought my first dildos. Yeah, I bought multiple types (length, girth, vibrating). I used them to fuck myself as often as I could. Living alone, there were no places off limits to do it. I enjoyed using them while talking to guys in online chat rooms.
And it wasn't long after that that I took my first real cock. I've been a cock-slut ever since. In my mouth is great, in my ass is mind-blowing.
My only regret as I said above is that I didn't start sooner!