Good question, hahahah, I haven't really thought a ton about this to be honest. I don't know if it was a singular person, it was more of a general realization that "hey I like boys more than girls."
That being said, my first actual crush was on a kid named Statton who was in my 7th Grade gym class. For a 12/13 year old boy, he was hot lol. I remember choosing my locker next to his on the first day of class so I'd be closer. And on the days when he wore his compression shorts, I was a happy boy