As I'm probably half way through my life now, death is something I think about but only in the sense of retirement and ensuring that I won't be destitute. About 10 years ago, I was very close to death, but that's a another story I don't particularly want to go into.
I've experienced death on several occasions. Some were of people who were close (maternal grandfather and a friend's mother), others not so close (paternal grandparents). Currently one of my uncles is very ill and has been in a home for well over a year now (though he was expected to die last summer - the old goat just fights on (and I say that with love and admiration!)). When I saw him at his worst last year, it was a shock and I broke down when talking to a nurse about his condition. That was a cathartic experience.
My own mother is declining gradually in her dotage. When I was living abroad she had to go to hospital. I, of course, assumed the worst, but the illness was not life threatening in the end. I do wonder, though, how long she'll live. So I am constantly thinking of death in that regard.
Also generally when you are young, death is not a consideration and the young act as if invincible.