I was 16 (grade 11), he was 14 (grade 10), boarding school, 1997.
I was deeply closeted and quite committed to the pretense that I was a hetero douchebro, even though I made no effort to mingle with girls (it was a co-ed boarding school).
He was new that year and lived in the dorm room next to mine with a very annoying kid named Tyler, who was so annoying that Pete (not their real names) started hanging out in my dorm as a way to escape him, and found that I didn't mind him being there and befriended him. At this time I had no designs on his ass, I was just being nice and didn't find him attractive, though he was a bit of a early bloomer. My main wank inspiration then and to this day was/is college jock types, and he was a small guy who liked marijuana and had a rebel attitude.
Long story short, he liked to wrestle, and found I liked it too. Before long, I started to want to fuck him, and it escalated to a point where I was DESPERATE to fuck him because the wrestling got more and more sexual as time went on. He would "jokingly!" press his ass against my crotch, would press himself right up against me and growl, it was unbelievably hot.
One evening my room mate is gone for a band thing and in comes Pete. I was focused on homework but we chatted a bit and I stood up to get a book off the highest shelf above my desk. Pete suddenly put himself between me and the desk and started running interference, batting my hands away from the shelf, keeping me from getting hold of the book I wanted.
I was sick of this flirty shit by then and reached around, grabbed his ass cheeks in each hand, squeezed, and lifted him up to sit on the desk by his ass. Once on the desk, I kept my hands there and worked my fingertips toward his asshole. He had his arms around me and was suddenly very still. I kissed his neck. He pulled back and looked at me and I said, "you need to stop teasing."
15 minutes later we were in the woods nearby and I was stuffing my dick in his ass bareback, doggie style. I actually had KY jelly I used to jerk off, so we had proper lube. Neither of us knew wtf we were doing though and it was just luck that there was no mess, he was clean, and soooooo tight. I didn't know about pre-play to get the bottom ready so I just pushed it in and it hurt him but he held on. I'm only around 7" but that was long enough to hit bottom, which also hurt him and at that point he almost did make me stop. He was a trooper though and I fucked him clumsily and came after maybe 2 minutes. We sort of cuddled after and I massaged his asshole by way of apology for the pain. Next time we tried, it was better. Fucked him maybe a dozen times.