I agree with the friends questioning the definition of "first time you had sex". So I am just going to bring the first association that came to my mind when I read the OP question.
My family was living in Buenos Aires, and we would travel every year to spend summer at the small town my parents were from. A cousin lived there, my same age. He was irresistibly attractive. I am not talking about me, he was irresistible for a lot of people, men and women. After he turned 15 he would fuck his teacher (a woman), several neighbors (men and women), and the town's catholic priest.
My memory was from a little bit earlier, when we were about thirteen years old. I was completely ignorant of sex, believe it or not. I would have erections watching TV, from women and from men, but would not understand what was that (my first cum had been a nocturnal ejaculation, I started masturbating after that). I remember walking into his bedroom when he was taking a nap, very early in the afternoon. I remember his smell intoxicating me, arousing me instantly. I think his smell was his super power, probably exceptional pheromones. I remember his respiration, in deep sleeping. I approached to his bed, I take his hands, put them on his chest without awaking him, getting close to his mouth to kiss him, and before even touching his lips, I remember the orgasm taking over me. It was the first time I realized my strong attraction for other boys. I started to arrange sleeping together with my cousin, and we would have sex without penetration faking we were sleeping. He became my first love, although he never loved me being too busy fucking half of the town. I would expend the whole year waiting for summer to be with him, masturbating and planning.
Later on, he moved from the small town to Santa Fe, a provincial capital, get into a relationship with a girl, and stop playing with men. He died in a car accident when we were 18 years old and I was In Buenos Aires getting into college. He was driving drunk with another male friend and two women, none of them was his girlfriend. He smashed the car on the front of a cargo truck.
His death was the final piece tat triggered my making peace with my homosexuality and finally coming out at age 21, including to my parents at age 23.