I remember a philosophy of science class I took as a freshman in college. The professor asserted confidently that we--almost all of us were traditional aged college students--did not really understand our immortality the way he--a forty-somethingish (I guess) professor--did and, by implication, that we did not have as close of an understanding of death as he did. I remember resenting that claim, not because I thought it factually incorrect (even at the punkish and arrogant age of 18 or 19, I realized that an older person might actually know more than I), but because this professor simply assumed that his claim was true. It was true of me, but he had no way of knowing which students in that class, if any, had had parents or close friends died, or who had witnessed one violent or near fatal episode, or who had undergone their own life-threatening situations.
I at 37 have known at least one person much younger than me who had faced the prospect of an early death through childhood cancer, and I suspect (because I've never really talked to him about it) that he had and has a much more acute sense of mortality than I did at his age or than I do now.
I'm reminded of the poem by Billy Collins "On Turning Ten," which ends like this:
It seems only yesterday I used to believeThere is much we don't know about the consciousness of others, and there is even less that we have the right to assert.
there was nothing under my skin but light.
If you cut me I could shine.
But now when I fall upon the sidewalks of life,
I skin my knees. I bleed.