Everybody goes through that. I used to cry a lot before falling asleep about the fact that I had to die some day when I was a kid. I really doubt your life is a third over considering that the life expectancy keeps getting longer though. And a lot of the first ten years were probably kind of a blur since your brain wasn't developed enough to have a great memory of what was going on.
Life is short, yeah, but you still have the rest life and if you can fulfill it properly that should be enough. Most old people say they're ready to go when they do, and you might find someday that it's a good thing it's ending. It's like eating cake- when you start you may be sad that eventually this cake will be over, but by time you're finished you're like, "Ok, ok- no more cake!"
Make your life a great cake and it'll all be worth it man.
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