This was from when I was in high school in the early 80's. I just turned 18 cupl months earlier. This is pretty much one of my 1st and ultimately my favorite sexual experience I ever had! Everyone mentioned was at least 18 at the time.

We were going on a 7-day school trip literally across the nation. From CA we flew to Wash DC.
There were about 65 students, so there were, as in any school trip, chaperones who watch over a small group of students each. When we met up at the school to leave for the airport we were split into groups and introduced to our chaperones. Turned out i drew the lucky straw! My group's chaperone was a slender, perfect hour-glass woman, mid-30's, with dirty-blond, shoulder length, wavy hair. She was wearing a knee-length sun dress w/wide folded collar w/the lapel folded open down to between her smaller-to-medium sized breasts (I'm guessing 32B?) that seemed to have permanent little pokies showing thru her dress! The dress was a off-white with pastel floral print, wrap-around with about 8 large buttons enclosing it down the center front.
In the V of her dress she wore a necklace with a pendant that showed an italics-style 10¹/².
As I was shaking her hand meeting her I smiled looking her in her eyes, shifted my gaze down to her necklace and purposefully made it obvious to look @ each breast, then back to her eyes and said, "Maybe even 11....!" Her smile curled up a bit on one side as she barely, almost imperceptably, tilted her head sideways with semi-nod.

After we landed and retrieved all our luggage we were bussed to our hotel which took about an hour or so. We learned that the hotel was booked solid with other groups from other states, but we were in the first 3 or 4 groups to arrive. Most of it was empty waiting for all other groups to arrive. Anyway, we got all checked in and made our way to the elevators.

And this is where it gets good....

So as I mentioned there were about 3-4 groups checking in. By now most of our group had scattered to the gift shop or up to see the pool or just wandering about the area.
I stuck around cause I wanted 1st dibs on my bed and to unload my suitcase and not drag it everywhere. I wandered over to the elevator and as we boarded I saw Mrs. 10¹/² (i think her name was Diane) already over in the rear corner on the right. So I meandered over to her, smiled and nodded and turned to stand directly in front of her. Meanwhile, people kept flooding onto the elevator. Too many probably causing us to cram in shoulder to shoulder!

Overly packed, the elevator doors closed and we began ascending. I reached my hands behind me to grab my left wrist with my right hand. In doing so, I accidentally (kinda purposefully actually) brushed my hand firmly against Diane's crotch!
At first she obviously startled away but there was literally no room to go as she was trapped against the back wall behind and in the left side corner. As I was about to turn and coyly apologize I swear I saw her eyes flash and twinkle and one corner of her mouth curled up in a half-smile and with her hidden left hand she grabbed my hip and pulled me in tighter to her body, literally pressing my hand against her soft nethers! My cock, which was hanging down alongside my right leg, grew rock hard instantly, trapped against my leg as it were!

Meanwhile behind me my hand firmly cupped Diane's crotch and she obviously enjoyed it by the way she pushed her hips forward, encouraging me to freely caress her pussy. Even thru her dress and panties I cud feel her crotch grow warmer and that she kept her bush neatly trimmed.

"DING!"
The doors began to open as we reached the next floor.

The dress Diane was wearing was a lightweight sundress. It was the kind that buttoned down the entire front w/large 1" or so buttons spaced about 6-8" apart. The 2 above her breastline, at the neck and mid-chest, remained undone as the dress was designed. So the topmost one buttoned was just at or below her breasts. Then midriff, about belly-button, hip level, just below crotch and last @ mid thigh.
Well when the doors opened and people started shuffling off and on the elevator and I used that jostling to cover my reaching down to unbutton those 2 lowermost buttons allowing me nearly clear access to the top seam of her panties. She pressed her hips fwd up and down ever so slowly and widened her stance slightly to enable my massaging her pussy. Now that her dress was opened I could feel her panties were sopping wet. My cock was almost painfully straining to stand upright but cudn't! It was definitely leaking at this point. I cud feel little drips on my thigh from it's precum weeping.
About 10 people exited but half dozen got on so we were still packed as tightly. The doors closed and as we began to ascend once more I slipped my hand inside Diane's panties running my fingers over her coarse pubic hair which I confirmed was neatly trimmed. Complete shaving wasn't "in" at the time, I think, but her manicured patch made my dick throb!
As i reached farther down I cud feel her pussy was absolutely soaking wet, her clit was erect and her lips parted easily as my finger passed across them. It slipped inside her just the tiniest amount and she pushed forward wanting it deeper as she breathed the lightest stifled moan! Her breathing was a light panting by now.

"DING!"
And the doors began to open.

My head was swimming and my cock was throbbing but my attention was on Diane's wet n slippery pussy. I pushed my middle and ring fingers in and they slid in without resistance. She gasped and pushed her hips a bit forward and downward and began barrrelyyy thrusting her hips back and forth literally fucking my fingers! She was slightly squatting and spreading her legs wider allowing my unfettered access. Her breathing was coming out shaky and almost whimpering.

The doors closed and I wasn't paying attention to how many people got on or off but the load was perceptably lighter. I just stayed plastered against Diane with my fingers curling inside her pussy. She started matching my finger strokes with her pelvic motions. Her motions were effectively rubbing her hardened tingling clit between the slit of my fingers and were becoming spastic thrusts which I could tell she was fighting to appear calm!
"Omigod I'm gonna cum," she whisper-breathed in my ear and I felt the first of her shudders ripple thru her body and felt her hardened nipples rubbing my back.

The dress was still kinda in the way so I slowly pulled out dragging my fingers scissoring across her super-hard clit and her breath caught again as I felt her body shiver! I was thinkin she was quite literally on the verge of a massive orgasm....I know I was! My dick was throbbing and actively leaking precum in my drawers!

Ding! As the elevator came to a stop. When the doors opened more people exited and none got on so we were becoming noticeable even tho there were still many people remaining.

As the doors closed I slyly unbuttoned the next up button clearing her dress out of the way. As I started reaching back inside her now sloppy wet panties she grabbed my hand and shoved my hand over her pussy the pressed my hand firmly into her but holding it still.
Another shudder and she almost failed at stifling her moan. I scissored her clit as she slowly pushed my hand across and my fingers back into her wet and slick pussy!
At this point I could feel her body trembling! She was losing the moaning battle with some light whimpering!
My cock was about to explode even tho it was still painfully trapped against my leg.
I dug my fingers deeper in and started the 'come here' curling motion again even tho at this point in my life I had no clue about a woman's G-spot.
Another shudder.....
Ding!
This was the 5th floor and turned out to be most everyone's that was left on the elevator. Ours was the 7th.
The doors closed and now it was obvious we were clumped in the back corner of the elevator. The other 4 or 5 people kind of turned their back to us purposely ignoring us even tho we were still trying but failing to remain "inconspicuous!"
Diane was visibly struggling to keep her breathing and hip gyrating in check; she was pumping her hips forward into my hand rhythmically as I fucked my fingers in n out of her dripping pussy. Which was hard cause by now my hand was cramping pretty badly!
Ding!....All the others exited!
We didn't even wait for the doors to fully close and with her left hand she started to furiously pump my hand into her pussy and across her clit letting out the long suppressed wail of ecstatic orgasmic "Oohhhhhh mmyyyyy gaaawwwddd.... !" At the same time she reached around my hip with her right hand and found my rock hard aching cock and grabbed it in a vice grip! As her pussy started flooding my hand her first pump on my cock sent me over the edge and my cock started pumping 3,4,5 times....but nothing was coming out due to being folded down against my leg. It was actually painful at this point!
Diane was was forcefully thrusting her hips in involuntary spasms while pushing my hand and fingers as far into her as she could all while singing/screaming/moaning one long, "Uuuunnnnnggghhhhhh!!"
As she was cumming she reached her hand down my pants to grab my cock which relieved the pinch-off opening the flood of pent up cumm spewing out in one long splurrrtttt making it feel like I was literally pissing cumm down my leg!
Ding! The doors began to open while we were both gasping for air each of us with cumm drenched hands plastered in each other's crotches!
Thankfully there was nobody waiting for the elevator and it was also our floor so we gathered ourselves buttoned up and headed for our respective rooms to clean up after agreeing we cannot be seen together especially in either's room as we could hear voices coming from some of them!
Before we parted I told her I wanted to fuck her for real and she actually agreed to accompany me to the hotel's restaurant on the top floor that night which unfortunately didn't happen.