So are you basically unable to think about death in a way that isn't far from you?

Yes, I pretty much am (except when driving or doing something similarly dangerous). At least, not about my death or that of other healthy young people in developed countries.

(Weirdly, though, I do often think about stopping functioning before legal death. It must be a combination of having read the parts of I Am a Strange Loop about Ronald Reagan's late life, my girlfriend working with Alzheimer patients on a daily basis, my grandpa starting to show long-term memory loss too, and, er, my having read the Yvain post I linked to in the previous sentence.)

I wonder how much this is common

I hear that's quite common among teenagers, at least according to the stereotype. (ISTR an EY post mentioning that, but I can't find it off hand.) I'm no longer a teenager myself, though.