Anyone else know what death was really young?

When I was 3, my great-grandmother died, and I attended her funeral. I remember pacing in circles around my grandparent's table as they explained that if someone died, it meant that they went away and never came back. I kept asking questions trying to understand it, and eventually I had a pretty good grasp on it.

I realized this was abnormal when I was reading a news article about the youngest person to commit suicide. I can't remember her exact age, maybe 6? The article claimed the story was dubious because a 6-year-old couldn't understand death fully.

I've had mental health issues for most of my life, and I remember being very young -- 5 at the oldest -- and hitting myself because I thought if I hit myself hard enough, I would die. Obviously, this was ridiculous, but I was very young.

But, yeah. Is this something common here, or is it maybe a byproduct of my mental illness?