Now granted - almost 100% of the time that I have sex with a guy it's Gary or someone I've known forever. There are those occasions that it's not, however. As someone that doesn't consider myself straight, bi, gay - but someone that certainly subscribes to the female species, even I find it odd that I have no problems taking the occasional cock in my mouth.
Some, I'm sure, would point to the time that I was 6 or 7 and had the experience with the older teen (see one of my oldest entries). Even at that time - that older boy's cock was perhaps the 3rd that I had touched. These things go a little deeper.
Before Gary there were the two brothers. I was perhaps 10 or 11 at that time. Before the two brothers there was Chris. Before Chris there was Sam. Sam lived three or four houses down from me and we used to play all the time. He was one year older than I was. We started playing together very young and my first memories of playing with each other's penis is as far back as when I was 7.
Back then we had no clue what we were doing. I knew if we got caught it would be "wrong" but I also knew it felt really good so I wanted to do it a lot. We would go anywhere we could. The woods, a treehouse, his bedroom. We pull our shorts down and stand in front of each other, reach out, and play with the other's penis. At 7 neither of us had a clue what we were doing, so it was simply rubbing and pulling.
We'd spend nights at each other's house and Sam would also want to do things under the covers. I remember that he was very aggressive. I also remember that Sam used to like to "play sex." He lie on top of me, both of us naked, and "hump." He loved doing this, I was indifferent as it did nothing for me. I preferred having him play with me.
I can't remember when it ended. That alone tells me that it didn't last all that long, maybe over the course of a summer? These seeds planted made it very easy for me to want to enhance things as I grew older. Once I understood what happened when you pump on my cock long enough made me long for anyone to do that for me. The aggressive nature of Sam led me to be aggressive myself a couple times with David (previous entries).
I think that most people (guys and girl) have those "play doctor" experiences while they are younger. When those happen over and over, and increase in intensity over time, this must fester a more accepting of things that society might consider "off beat."
Don't even get me started on the nature versus nurture aspect of why people go down a left or right path in life. I do think, however, these experiences certainly help push you along.