I can't remember a specific age, but I think I was around 10. If I remember right I stumbled across ad that lead me to porn and I was definitely interested.
A helluva lot younger than when I actually found the nerve to do anything about it! That's why I'm such a loli perv - re-living lost opportunity. Grown ups vs loli doesn't do much for me, but shota/loli makes me stupid(er)!
Definitely from a very early age before finding out in sex-ed why I was so horny all the time. I became fascinated when a girl followed a dare of pulling down her panties, lifting her skirt, and bending over in the playground. I had no clue why that was so hot.
Didn't know what sex was, but had stirrings and motivation at 4. I don't recall any "bad touch" before that so just natural curiosity and desire of innocent youth I suppose.
I think I was about the same age and I also used my pillow but I don't think I know about sex few years after when I hit puberty and started talking to mu friends about jacking off and all that