Ooh, this is a tough issue. I find myself worrying about it more and more, actually. I sometimes even wonder if our adopting was ethical.
But then, as an RN, I see a lot of crazy stuff. We once had a 28-year-old grandmother when I worked in labor and delivery. And just recently, we've had 3 patients in their 20s and 30s that I've worked with who have less than a year to live due to cervical cancer. In some ways, we have lived in an ideal time, too, in that, in the past, people regularly died of infectious diseases--you could have a 30-year-old dad die when you were 10 after something so seemingly "small" now, as the flu. These kinds of deaths happen less often now, but still I am sometimes struck by how difficult people's lives can be, and how quickly things can change. There are no guarantees for anybody, at any age.
Of course, the chances are better for younger people . . . My dad was my age when I was born, so I just hope to keep on ticking along as long as he did. But, yes, it's difficult and scary.