The results of this year’s Jazz Critics Poll — NPR’s fourth annual and my 11th, counting from its 2006 inception in the Village Voice — slightly resemble those of the last two. Henry Threadgill, Jack DeJohnette, Mary Halvorson and Vijay Iyer all are repeaters from last year’s Top 10, and Steve Lehman and Wadada Leo Smith are back from 2014’s, when they finished No. 1 and No. 2. With Smith, Threadgill and DeJohnette all over 70, and Charlie Haden 76 when he died two years ago, the average age of the musicians in this year’s Top 10 might be the oldest since ’06, when Nels Cline (No. 7 this year and 10 years older) was the baby at 50.