Recruited back to the University of Pittsburgh School of Law from a post at Duquesne University, tax professor William J. Brown found his return to the academic mainstream blocked by administrators who wanted younger teachers, according to an age discrimination lawsuit filed in U.S. District Court today, reports the Pittsburgh Post-Gazette. Mr. Brown, 73, of Squirrel Hill, joined Pitt’s law school in 1968, the complaint said, and was quickly granted tenured status. He stayed for 30 years, then left and soon took a post as the director of the Graduate Tax Program at Duquesne’s business school…