Interesting question and premise.
I can remember looking at some bottles underneat the sink in the kitchen and wondering if I swallowed them if it would kill me. I don't know how old I was, but I was under 5.
When I was 2 1/2, my grandfather raped me and afterward said, "If you tell anyone about this I'll kill you."
My parents had a lake house when I was little, and one night we were out there. I remember it was a clear night with a full moon. I came out of the house and saw all the grownups standing by a campfire. The memory is a bit shaky for me, but the next thing I remember is one of the men holding a puppy the back of its neck. I remember hearing the puppy crying in pain. The man had a knife. The next thing I remember is holding the puppy in my arms and running. I can still hear the sound of my feet running on dead leaves, so it must have been autumn. Someone was chasing me and quickly caught me and threw me to the ground. I then saw the puppy being eviscerated.
So certainly by the age of 4, I was aware of death. It took me until I was almost 30 before I was aware of life.