By Mitra I. Arthur Credit: Photo: Elizabeth Gillis/NPR Buddy Guy displays a youthful spirit during his Tiny Desk that makes you question if he really turns 90 this year. Once the music starts, his subtle speaking voice transforms into a mighty instrument, demanding your attention. Guy wails on his polka dot Stratocaster, reminding us of his skill and showmanship. The title of his latest album, Ain't Done with the Blues, is not only apt but defiant. The elder statesman of blues is the last standing among his fellow architects of the genre like B.B. King, Muddy Waters and John Lee Hooker. Throughout his career, he has collected every accolade possible, including a Rock and Roll Hall of Fame induction, a Kennedy Center Honors award and the National Medal of Arts. He recently took home his ninth Grammy Award, this time for best traditional blues album. His set starts with his rollin' 1991 classic "Damn Right, I've Got the Blues" and moves into "Hoochie Coochie Man," both songs a must for any Guy performance.…