David Remnick talks with The New Yorker’s literary guiding lights: the fiction editor Deborah Treisman and the poetry editor Kevin Young. Treisman edited “A Century of Fiction in The New Yorker,” and Young edited “A Century of Poetry in The New Yorker,” both of which were published this month.  “When you asked me to do this,” Young remarks to David Remnick, “I think my first response was, I’ve only wanted to do this since I was fifteen. . . . It was kind of a dream come true.” Treisman talks about the way that stories age, and the difficulty of selecting stories. “The thing to remember is that even geniuses don’t always write their best work right right off the bat. People make a lot of noise about rejection letters from The New Yorker that went to famous writers, or later-famous writers. And they were probably justified, those rejections.”