what age you started your very first relationship?

When I was in middle school, a guy who I had a crush on told me we dated back in daycare. I don't remember it. The earliest I remember dating was when I was 12. I started dating a girl my age during the summer, the year I started middle school. I was so surprised to see her there since I've never seen her at school before (maybe that's because we went to different elementary schools).
We met through her grandmother. At the time, my mother was neighbors with my now ex-girlfriends grandmother and I would sometimes go over there whenever my mother does. This grandmother looked rather young and fit. The grandmother had called one of her granddaughters, thinking that she knew my little sister, since one of her friends and my little sister has the same name. Her grandmother called her over for a sleepover with a friend, only to find out that her friend wasn't there. The night I had spent over at her grandmother's house with her, we slept in the same bed (me, her and her grandmother). We both couldn't sleep. I was the kid who could feel people's vibes, especially whenever I'm alone with them and they're awake. I lied in the middle, she was on a side of me while her grandmother was on the other side. I had/felt this vibe that she wanted to kiss me or something. I didn't act on the vibe. She asked if I was asleep and I told her no. I forgot what she said afterwards, but I recall her asking if we could have sex. I agreed, not really sure of my sexuality at the time (I wasn't worried about my sexuality, since I had never thought about it before). We did it on the bed while her grandmother was asleep. I liked it, I enjoyed it. Her grandmother didn't wake up. From that night onward, we started dating, but not publicly.
She wasn't really a girlfriend. I allowed her to have sex with a female classmate, mostly because I didn't know how to be a girlfriend. Then when it was time for me to spend the night at her house, I saw that she was already dating someone, an adult actually. Yeah, I was hurt, though I had always been selfless, and sometimes selfish.