REVERE – The 20-year-old suspect charged with shooting to death a 17-year-old outside the Revere Beach Carnival in 2003 was sent Tuesday for a mental health evaluation before his trial is set to begin, authorities said.Lincoln Latham of Roxbury is charged with the shooting death of Charles Deon Ajene, 17, of Chelsea. Ajene, who previously lived in Mattapan, was shot multiple times in a car at the corner of Ocean Avenue and Revere Street shortly before midnight June 27, 2003.The two young men “and their associates” had an ongoing dispute that led to a verbal argument at the beach, Suffolk District Attorney spokesperson Jake Wark said.”That argument, investigators believe, led to a fatal confrontation a short time later,” Wark said.State and Revere police arrested Latham a short time later during a traffic stop at Mahoney Circle, where police recovered a firearm from the vehicle.