This was just one of several experiences I had with a very sexy high school girl. I think she was only 17 at the time.
When I was a freshman at an all male college in Michigan, I hooked up with a high school senior. She was a really hot looking gal with a terrific body. She loved to makeout but wouldn't let me fuck her. We would kiss and smooch for hours. She would let me feel her breasts and suck on her nipples and every so often let me finger her pussy.
When I would get out of class I would go to her house and we would mess around until her parents got home from work. Then I would have dinner with the family, which included her grandmother who lived with them. After dinner we would all go watch tv.
The living room wasn't that big so mom and dad and me and the daughter would sit in the living room. As I recall, dad had his own chair and mom, daughter and I would sit on the couch. Grandma had a favorite rocking chair that was actually in the adjacent room but was positioned so she could look through the large archway into the living room and watch tv which was positioned in a corner.
Where I was sitting I could only see grandma's feet rocking back and forth as she worked on her knitting and watched tv.
The folks were notorious about going to bed early. They were usually up the stairs by 9 or so leaving the daughter and I in the living room and grandma rocking away in the next room.
As soon as the folks hit the hay, the daughter and I would immediately start smooching up a storm. I am not sure why, but she would let me go farther with her sitting in her own living room with grandma ten feet away than she would when we were alone. Probably because she knew I could take it only so far. There was no chance I would try to fuck her but we did just about everything else.
On one particular evening, she was much more receptive than usual. She had a sweater on which I pulled up and then I unhooked her bra in back, which allowed me to slip it up over her breasts. Then I could suck on those beautiful nipples as I kneaded her full breasts.
After an hour or so of this, I was so hot I thought I was going to burst. So keeping one eye on granny's rocking feet, I slowly unzipped my pants and took out my erect cock. I took one of her hands and wrapped it around my straining prick. Then with my hand on top of hers I started moving her hand up and down the length of my bone-hard penis. After a few strokes she took over on her own and began rolling my foreskin back and forth over my cockhead.
I am actually partially circumcised but the doc left about half my foreskin intact. So it is possible to roll it up to where about 3/4s of the head of my cock is covered and then to roll it back down so the whole purple head pops free. And she was getting into the rhythm of expertly masturbating my cock. I had pulled my jockeys down under my balls, which caused them to jut up where she could cup them in her free hand. Holding my balls in one soft hand while she jacked my shaft with the other was driving me nuts. At only 18 years old I knew I couldn't last long as her fingers and hand flew up and down my prick.
However, the thought that granny could get up at any moment to go to bed or get a drink of water was somewhat distracting because if she did, there was no way I could stuff my erect prick back in my pants and get them zipped up fast enough.
But my girlfriend's expert manipulations soon overcame any concern I had for granny and I could feel my orgasm start to build in my balls and pretty soon a geyser of white cum spurted from the tip of my purple prick. The first blast shot all over the front of my shirt and that was quickly followed by several more really powerful and voluminous spurts of cum that literally drenched my shirt, my pants, and her hands. I think it may have been one of the messiest orgasms I ever had. And of course I had to maintain total silence while having this incredibly intense orgasm.
Fortunately there was some Kleenex on the coffee table and we quickly tried to clean up what we could but of course not much could be done about the cum that was soaking into my clothes. Once I got as much cum mopped up as I could, I zipped up, quickly kissed her goodbye, called out a good evening to granny, and got the hell out of there. I am still wondering if granny couldn't detect the very distinct odor of cum?.