9/11. I was in 8th grade in my first period class. One of the other teachers came in the room and told us to turn on the TV because something was going on in New York. We watched it the whole rest of that period, and then a lot of us huddled up in the old Home Ec room and watched the news coverage. I saw the second plane hit live on TV. One of my teachers told us things were about to change for everyone, and about 30 minutes later they made us shut it off and sent us back to class.
My first time driving on my own. I was entirely terrified and just kept feeling like I was doing something illegal. Fortunately that passed quickly
The day I realized my father was about to die. I was 15. He had cancer and I knew he was
close to the end, but this was not long after the doctors told us there wasn't anything more they could do for him. He had been under at-home hospice care for a couple of weeks by this point. I won't go into the exact details, but it became extremely apparent that he was very close to dying. Every second of that situation is permanently etched into my brain.
Moving out of my mother's house when I was 18. We had a very tumultuous relationship after my father's passing, and I left home about as soon as I was able to. I had a friend from PA (900 miles away) who moved me up there and the part I remember 100% clearly was walking into the very small bedroom in the shitty duplex they had just rented and wondering just what the fuck I did. I had never been to Pennsylvania, I knew nothing about the state or the north or snow. I didn't know the other roommate at all. Fortunately, that ended up being probably the greatest choice of my life and set me up for my future.
Flying in my first small plane. This was actually a discovery flight when I randomly decided one day that I wanted to get my PPL. I had tons of commercial flights before that, but I remember looking out the window while turning onto the runway and thinking it felt like being in a go-kart since we were so low to the ground.
I'm sure there are probably more of these moments in my life, but those are the ones that immediately came to mind.