Is it this one? I loved it. It was one of the stories what bring me to this genre

Exactly those were my dreams when I was 13y/o
Danielle 1
One summer, when I was about 17 years old, I used to hang out with my
best friend on his deck, shirts off, soaking up the sun and shoooting the
breeze. We explored the issues of the day and the questions that have
tantalized philosophers since the beginning of time. But one sweaty
afternoon has always stood out --it led me to the most intense fantasy I
ever had...one that that was a constant source of arousal at that age and
one I revisit from time to time. My friend had a younger sister,
Danielle. Danielle was about 12 at the time-maybe 13, but I don't think
so.
That hot July day, the sun was shining strongly on the deck. My
friend and I were dressed for the occassion and were sipping iced teas.
We both had taut, muscled 17 year old bodies--Ah, how I miss that earlier
version of myself. Young Danielle was shorter than I am, which is not to
say much because I topped out at about 5'5". She was in a one piece
bathing suit. Her brothers were avid weighifters at a time and age when
that was unusual. Danielle may have touched some of the lighter weights,
because she was fairly sinewy--but it might have been just good genetics.
My friend got up and went inside, closing the sliding door behind him.
Danielle began to try to get my attention. She asked me to flex my arm.
I declined, althogh modesty about my body is not one of my better
qualities. I enjoy showing off, but I have always been discreet, and
feign modesty or shyness when asked to display myself--perhaps because it
seems unnatural, or maybe I'm more uncomfortable than I would like to
admit. After a little pestering I complied and flexed. My arms were, I'm
guessing, a little over 13" then, but had nice peaked biceps. Danielle
began to pinch me--my chest, arms, wherever she could poke her hand, while
I tried to keep her hands away. I got up from the chair and headed for
the door, still parrying Danielle's curious, teasing probes. As I walked
away and got between her and the door, Danielle grabbed hold of one of my
buns, pinching and twisting the tight hard flesh now caught in her
fingers. Startled. I knocked her hand away, but she grabbed more flesh
with her other hand, sharply twisting my virgin gluteal muscle. At this
point, I startled myself, as I realized that this was having an
extraordinary, arousing effect.
I became dizzy, lightheaded, and I was aware that my penis was
beginning to stiffen. Afraid, I grabbed Danielle's arm and told her to
stop. When I let go she immediately pinched me again, then swung to my
front. She pulled at my shorts (I was wearing cotton athletic shorts, the
type with built-in underwear-like a bathing suit). Danielle clutched at
the waistband and pulled it away from my body. Again, I knocked her hand
away and reached for her wrists. She cried with delight and derision, "I
saw your thing." Then she reached for the front of my shorts. I stopped
her hands cold. At that moment, my friend threw open the sliding screen
door and barked, "DANIELLE, STOP IT!" Danielle retreated, her face
registering frustration and disappointment.
Then Danielle decides to take control of the situation. "If I'm going
to really have fun with Eddie, I need to be stronger than he is. Then I
can have MY way with HIM!"
That night Danielle goes into the basement where the weight set is
kept. She looks at the iron dumbells and the iron plates across the
floor, the bench and bar above it and the leg extension at the end of the
bench. She quickly makes her mind up. Her parents are on vacation and her
brothers have both gone out for the evening. She calls to the family's
Latin housekeeper, "Dora, come here!" (Danielle's father is a very
successful, suburban doctor, and her parents spend very little time at
home. They hired a live-in maid to care for the house and cook for the
children).