This spring, American treasure Willie Nelson will celebrate his 90th birthday. In a career that goes back to the ’50s, Nelson has never been inactive. He still tours, and he still records; just last week, Nelson announced plans to release a new album, the Harlan Howard tribute I Don’t Know A Thing About Love. Willie Nelson has always been country artist, but his music has transcended all known boundaries, and you can see that appeal in the stunningly broad lineup for Nelson’s 90th birthday celebration, which will come to the Hollywood Bowl in April.