Me and my sister used to masturbate together as teenagers.
I was sixteen and my sister was eighteen at the time, and we have always masturbated together from when we were teens. I have learnt a lot from her about the female body, things that I could not learn from school or my parents, and I believe that she has contributed to me having the great sex life that I have with my girlfriend today.
This one time I returned home from playing soccer and was still in my kit. I ran upstairs, because I needed to pee, when I noticed that the door was slightly open and steam coming out from the crack. My father had not fixed the lock on the door since it broke a few years earlier, so I have often been walked in on by my sister when showering or bathing. This time she was in the bath with her eyes closed just relaxing, feeling the steam on her hot wet body. I couldn't see her pussy because of the soap, but her beautiful breasts were sticking out of the water and were wet and soapy.
The sight of a wet female body always gets me hard and I immediately got a huge erection. 'God your a horny fucker' she said opening her eyes, seeing my hardon in my shorts. 'Come over here and I'll sort you out' It didn't take me long before I was standing over the bath and she had my shorts down and was holding my erection in her right hand 'Blimey you are getting bigger' she smiled as she slowly stroked my cock with her wet soapy hand. This was blowing my mind.
As she wanked me, I was gradually getting harder and fatter with her strokes of my shaft. With her left hand she took my balls and gently fondled them. I could not take my eyes off her tits until I couldn't take it any longer, and had to caress them as she wanked me. Her hand wanking my cock and me stroking her wet breasts meant it wasn't long before I had shot a huge wad of cum all over her hand and into the bath. 'OHHHH that was fantastic,' I said as she squeezed the last drop of cum out of my now semi-erect cock. I stood there for a few seconds savouring the moment then she said 'Now go away and let me have my bath in peace' I wasn't arguing so out I went to my bedroom and lying on my bed stroked myself off again, thinking about my sis drying her naked wet body in the room next door but one.