The first instance of shared masturbation was with a neighbour girl, Wendy. It was a hot summer day and I was preparing an exam cram lesson on her back porch for her brother Bill, a high school football buddy. He had to take a summer school course to play football the next year and it was a subject I had aced so I was giving him the fast track to get through it and move on. He was due back from his summer job later so I thought I'd wait around until then. Bill and I were both sixteen and were well used to being teased by Wendy, a precocious but gorgeous 15-year-old, we openly called 'Jailbait.'
Wendy looked like a 19-year-old vixen. She was a sudden bloomer and was beside herself with hormones but knew none of the guys would try to break her cherry, given her age.
She came in from the pool in her bikini and threw herself across the lounge in front of me, drying herself off with a towel and leaving the towel across her waist. I went on reading and I ignored her but after a while noticed a strange writhing and jerking motion under towel. Her eyes were almost closed. At first I thought she was dreaming but pretty soon it became obvious that she was doing a pretty poor job of surreptitiously jerking off in front of me. I said something sarcastic like 'So does that feel good, babe?', thinking I'd startle and embarrass her.
Casting off the towel, she turned her head and said 'I thought you were made of stone!', now openly gouging her fingers under the side of her bikini bottom. 'But at least I can get rid of this...' she said, pulling off her bikini top and bottom and spreading her legs. She turned to give me a better view and smiled as she now used both hands to caress her labia lips and clit while rubbing her nipples. Unable think of anything further to say I sat there motionless only then aware of the pressure that the book on my lap was making against my huge erection. She was moaning, cupping her breasts and lifting her bottom from the lounger as she became more intent on her efforts to get off. I could hear the sloppy wet sounds from her fingers against her labia and the sounds of her fingers going in and out of her vagina, punctuated more loudly by longer cries and moans.
After a minute Wendy looked over, smiled and slowed her frenzy. Having not yet come she opened her eyes widely, smiled again and asked if I was going to 'get it out' because I looked like I was now 'in need of a serious jerk'. I didn't need to be told twice and in a second I had my cock throbbing in my pumping hand. I had never had such a hard 'veiner' Already the purple head was oozing pre-cum ejaculate and I could feel the momentum building in my balls! Wendy just went back into a frenzy, saying 'I want to see it spew!'
I shot a load onto her chest, onto her left thigh and dribbled the rest onto the floor between us. When she saw that, she tossed her head back and shuddered in orgasmic spasms, legs twitching, and letting out an unending UnnggaaahhoohooOOOOO!!
When we heard the door open at the front of the house she bolted for the pool with her bikini in hand and I zipped up. For a second I just sat there, looking at the wet spot where she sat, very happy that I had 'come' over. She and I eventually laughed about it years later at college.