Despite my age, my experience is somewhat limited. For example, in real life I've never had sex with a man, just a couple of near misses, for example...
About 50 years ago, 18 years old and horny as hell, I'd just finished my delivery round and went into a brick-built public toilet. I saw a hatch to the roof space and wanted to climb up and see if I could spy on the women. Embarrassing now, but I was young and alone... Anyway, it never came to that: beforehand, I wanted to check that there was nobody in the cubicles - well, one was empty, but as i pushed on the door of the other one, someone was in there and blocked it - neither of the cubicles had working locks. So, I went out and came back a few minutes later.
Tried the door again - he was still in there, and I was pretty sure what he was doing... That's not what turned me on at that age, I just desperately needed to wank, so I went into the other cubicle and let my pants down so i could grab my already hard dick, cup my balls and start tossing off. The door was at my right side as I stood facing the toilet bowl, and I had my foot blocking the door.
I heard him going out of the other cubicle and then unexpectedly he pushed against the door. I held it shut, but then he pushed much harder, barged in and closed the door again - he was standing next to me with his erect cock in his hand!
And what a monster. It wasn't so much longer than mine, which was still standing hard, almost ready to cum, but it was at least twice as thick. I'll never forget the bulging veins and the red tip of that enormous dick right next to me. Both of us were uncircumcised. I was scared stiff! Scared, and stiff! ;-)
He stared at my long thin prick (much better looking than it is now) just as I had been staring at his, and asked me: "Do you want me to suck it?"
That's the point at which the panic overcame me and I wanted to open the door. However, just at that moment, we heard someone come in to the building, and we had to keep quiet until he had (literally) pissed off. Then that was it, we went our separate ways without cumming, I was frustrated and still a bit scared.