I grew up JW, believing I would never die. I never came to terms with my mortality until about one year after I parted ways with the JW's.
I reckon most people learn about and accept their mortality when they are younger. The JW's delay that maturation process.
I read about a study last year that people between 60-70 years old are actually happier and more satisfied than younger adults. Why is that? Maybe they've come to a point in their life when they really know who they are, and don't fuss about little annoyances and concentrate on enjoying the "big picture" (if that makes any sense).