I guess I really don't know the first time I masturbated, because my earliest memories included touching and squeezing and feeling good. But my first orgasm was an event I will never forget. I was a young teenager. My older sister, Judy, had come home from a well-known art school back east. She had been telling the whole family about her life-drawing classes with nude models and how wonderful it was. She was telling everyone how beautiful the human body is and a wonderful art form. Judy insisted it was not a sexual thing. She came into my room late one night and wanted me to pose for her. She said she needed to practice her drawing and talked me into modeling. I kept covered with my bed sheet and she kept telling me not to be ashamed, my body was beautiful and she had seen plenty of nude models, both male and female. Judy said I wouldn't show her anything that she hadn't seen before. I reluctantly let her pull the sheet away from my naked body. I was very nervous, as you can imagine. She told me to relax and kept talking to me, making me less nervous and ashamed. And I have to tell you, the more relaxed and comfortable I got, the more excited my cock became. Having my sister looking at my nakedness made my cock stand up in no time. I think she thought her little brother has really grown up while she was away at school! She told me it was alright, to just relax and let her draw. She kept talking to me, afraid I would back out. She told me how nice I looked. I was feeling a wonderful rush inside my belly like I had never felt before.
Judy drew several pictures and then started concentrating on my penis. She said it was a fine example and that I should be proud. I was! She then just drew pictures of my erect penis and scrotum. She had me change positions several times. Finally she reached over to 'arrange me.' She touched my cock and it jumped in her hand. She seemed to like that and continued to 'arrange me.' I think I moaned and that is when Judy started to deliberately rub me up and down. I couldn't believe she was doing that, and couldn't believe how wonderful it felt. I forgot about everything else just then and just let her have her way. I could feel intense surges through my body and could feel my balls getting tight and feeling extreme pressure, and then I blew my very first load. It was so intense it was painful and I suddenly got scared. She told me it was ok and helped me clean up. She left my room that night and we have never talked about it again.
That was over forty years ago, and I have never told anyone and I don't think she has either, and it has never come up between us again. After that night I often thought about it and fantasized about it when I jerked off. I bet she has too. I never saw those pictures she drew of me again. (I wonder if they are hidden somewhere, and she gets them out occasionally to look at them.)