Tuesday is J.D. Salinger’s 100th birthday, but Holden Caulfield is still 17. The iconic teenager of “The Catcher in the Rye” is forever suspended in the amber of our youthful alienation. Although a few pious schools continue to ban Salinger’s only published novel, for millions of adults, a faded copy of “The Catcher in the Rye” is a sweet teenage treasure, as transgressive as a trophy from band camp. Ninth-graders who secretly read the book with a flashlight when it came out in 1951 are now in their 80s. To read it again as an adult is to feel Holden’s...