A grim milestone: The number of American dead in Afghanistan crossed 1,000 on Tuesday after an attack on a convoy killed five U.S. soldiers. The rate of death is alarming: It took seven years for the first 500 American deaths; the second 500 have all taken place in fewer than two. The average age of the American dead is dropping as well: Between 2002 and 2008 it was 28; last year, it was 26; and so far this year, it’s 25.