You say:

"By definition, the chance that you'll die before your projected life expectancy is 50 percent."

Let me "baby" you through this. Say you have three 65-year old women: one of them lives six years, one nine years and one thirty years. Together they have lived 45 years past 65 - their life expectancy at 65 would have been 15 years.

Two of the three lived less than their 15 year life expectancy.