Late post to this thread... mine started at age 4ish. It's kinda hard to remember, I blocked a lot of it out.
Basically, my sister, who was 16 or 17 at the time, was bulimic. One day, on Halloween, I was at a little holiday party at my preschool. My mom got a call from my sister and my mom told me we had to go home immediately. She didn't tell me why. When we got home it turned out that my sister was p*rging and had choked while doing so, so v* was all over the toilet seat and in the hallway and on the baby gate. When I walked down the hall to the bathroom, I froze, and at this point, she was still v*ing because she was choking. I couldn't move, I was just staring at her and watching my mom clean up the v*. I didn't feel scared or anything but I definitely didn't go into fight or flight, just freeze. I was like a deer in the headlights. I guess you could say I had some type of cognitive change starting then. When I could finally move I asked my mom what was happening because I didn't understand. I had never had noro or anything (at least not at an age that I could remember at the time as I was only 4), so I didn't understand. I also didn't know that my sister was bulimic and that that's why she choked at the time. I remember feeling really embarrassed and like my face was hot when I was talking to my mom. I was looking down at my feet like I had seen something dirty.

Anyways, so from then on I became petrified of v*. I got noro right after I turned 5, then noro again and food poisoning once when I was 10, but nothing ever since. The whole thing is really weird and layered because that sister who was bulimic molested me as a child and then took her own life when I was 6 and I deal with OCD and an eating disorder of my own.