NEW YORK - James Levine, the music director at New York’s Metropolitan Opera for 40 years, will retire this year for health reasons, the Met announced on Thursday. Levine, 72, who has battled Parkinson’s disease and other health issues in recent years, will step down at the end of the current 2015-16 season in May. He will be named music director emeritus and will continue to work with the Met’s young talent development program, the Met said in a statement. His successor at the Met, one of the most prestigious opera houses in the world, will be named in the coming months.