This event happened one afternoon when I was 13 and round at my friend Andrew's house. He had a sister called Sue who was about 18 months younger than the two of us, a friendly girl who I quite liked.
This afternoon Andrew and I were playing cards when Sue came in and asked if she could join us. We said okay and Andrew suggested that we play strip poker. I wasn't too keen but Sue was happy enough so I went along with it. After a while I was down to my underpants, while Andrew still had his shirt and pants on and Sue was down to white vest and navy blue knickers. I was nervous and embarrassed at the thought of stripping off completely in front of Sue.
Sue lost the next hand and took her vest off and I saw her bare chest. She had not really started to develop any breasts but I noticed that there was a slight swelling and puffiness around her nipples which appeared larger than a boy's. The next hand I lost and I was told to take my underpants off. I tried desperately to avoid doing it, but Andrew and Sue insisted they come right off, and so a few moments later with cheeks burning in embarrassment I was naked. Sue shrieked as she saw my 'willy' which was still quite limp and small.
She then said 'Would you like to see my pussy?' and before I could reply she had slipped her knickers off so that she too was naked. She sat facing me with her legs apart giving me a clear view of her practically hairless slit, there were just a few tiny wisps of dark pubic hair beginning to show. She was the first girl I'd ever seen in the nude and whilst I felt it wrong to stare I couldn't help but look at what she was displaying to me. I also realised that I was starting to become aroused by it and getting hard.
Andrew said I should have to pay a forfeit for losing and Sue could decide what it would be. She said I had to let her touch my 'willy'. I was still too shocked by things to say anything so she got on her knees, reached out, and took hold of my penis with her left hand. She squeezed it and then pulled the foreskin back exposing the purple head and I became fully hard. She giggled and said that mine was bigger than Andrew's. She then said 'Shall I wank you, yes, I think I should'. She started to move her fist up and down my penis pulling on the foreskin as she did so. Although I'd been masturbating for quite a while at my age, this was the first time anyone had ever done it to me or even seen me with an erection.
Sue began to increase the speed of her pulling and I could feel the tension building in my penis. I noticed that her right hand was clenched between her thighs over her pussy. Andrew had also stripped off by now and was masturbating his erection while he watched Sue with me. Eventually I couldn't hold back any longer and I spurted a stream of cum all over Sue's chest. She again shrieked before giving me a big grin, she then gathered up her clothes and headed for the bathroom to clean up. Andrew had also cum soon afterwards.
Later Andrew told me the card game was Sue's idea since she had wanted to see my 'willy'. He also said that he and Sue had been naked together before and she liked to see him get erect and she would then wank him off. This was just the first of several enjoyable events I had with Sue as we grew up.