MOVIES THAT MATTER, FRIDAY, MARCH 19 AT 7 P.M.: The movie for March 19 is called YOUNG AT HEART. Coldplay, the Clash and Jimi Hendrix will never sound the same once you've heard the Young@Heart chorus, a group of Massachusetts senior citizens who thrill audiences worldwide with their unusual—and unusually poignant—covers of rock songs. Stephen Walker's humane and heartwarming documentary, which premiered at Sundance in 2008, follows the elderly ensemble as they prepare their latest show for public performances.