Well let's start when I was 13. My twin sister and I had always shared a room. We had a night table between our beds, but at 13, she was just getting some tiny tits. I could see her at night, moon light through the window, and she would pull her top up and play with them in the dark. She had no idea that I could see her. One night, summer, hot , I pulled my covers off, she had already done the same, when she pulled up her night shirt and started playing with her tits. My dick got hard, growing to it's full size of almost 6 inches. The buldge in my shorts was plane to see, and while I lay there watching her in the darkened room, she saw it. She quickly pulled down her shirt, and I could not help grouning in dissapointment. She asked if I was watching her, and I replied, I have been for several months now. She got out of bed, came and set on the edge of mine asking if I enjoyed the show?? I said of course, but would have liked to see more. She said take your shorts off first, and I will show you more. Soon both naked, and she was sucking my dick. I filled her mouth, she spit it out on my tummy, and I went to clean up. When I returned to my bed, she was on her back, legs spred wide, said my turn. I then proceeded to eat out her pussy, her cumming me sucking in every drop of her cum. I kept eating that tiny pussy, and then she pulled me up over her body. First time for both of us, and over the next few years, we learned how to give each other much pleasure. By the end of H.S. my dick was about 7 inches, fat, and she was bringing her friends over to get fucked. I too, brought my friends over for her to fuck. One weekend, we were 16, fokes gone for the weekend, my best friend came over with his sister, 14, and we had a time fucking each other, trading off with each other. His sister told me they started fucking when she was 11, but she liked my dick better, not because it was bigger, both about the same size, but said I lasted longer, and felt better inside her. I was his best man when he married my twin sis, and about a year later, he was my best man when I married his little sis. We still get together, but after marriage, no swapping any more. We really pretty much stopped after that weekend. Two or three times a year, I would fuck my twin through the rest of H.S., but only if she and he could not get time together, and the same with me and his sis. We doubled a lot back then, so if we could not get with him/her I woulf fuck sis.