Howard “Louie Bluie” Armstrong has been performing for most of his 91 years, ever since his father carved his first fiddle from a wooden crate. Leah Mahan’s Sweet Old Song plays like one of the ballads that flow effortlessly from the funny and irrepressible Armstrong. At the film’s center are the two great loves of Howard’s life: his music and artist Barbara Ward, age 60. Their two-decade romance has been a creative partnership yielding new work and an outpouring of memories. Their experiences are captured in Armstrong’s lively paintings and stories of nearly a century of American life. As they take on life’s challenges, Howard and Barbara defy our most basic assumptions about what it means to grow older.