In porn? At about age 11, in a magazine.
In action? Just before I turned 14. I was with a group of kids who were very sexually active. I had gotten head from girls many times but was still a virgin at that stage.
There was one fat white girl who loved to 'mushark' (verb) as it might be called now. I was hanging with a group of others kids and this one black guy who was around sometimes decided to give a show. He got head from the girl and fucked her in front of us others.
He was not well hung, not all men black or otherwise are, and he was in the matter to just satisfy himself. He fucked her for about 12 minutes and came in her. He joked "ten minute brother for a $2 hoe" afterward.
I loved the contrast of his dark skin on her pale skin however. I had seen people fuck before. I liked the look of his dick slick from her pussy, again the contrast there.
I was a bad kid and was in group home (or later detention halls) for much of my teen years. The group homes had female and male teens there.
I would see a grown black man fuck a teenage girl not even a year later. He was moose hung and she was black owned. She blew me at times even when I'd watch them go at it. He was a staff member and she a patient. If there was a male along with the female and a male staff member, that did not raise any red flags about have a male staffer be with a young girl alone. Guess the administrators never thought the teenage boy would join in, or lie about to cover up, any sexual misbehavior going on.
Me and some other guys were the 'cover' at times for these two fucking. Like I said, I'd get BJs so I was cool with seeing her get balled to her limits by this big black dude. Fun times. I did not care about the IR angle really. That was hot but to me it was more about the age difference and his being an authority figure.