Two more teenagers have been arrested in an allegedly unprovoked attack that left a 64-year-old city school administrator with several broken bones. The 15- and 16-year-old Stamford Academy students were charged Monday with first-degree assault on an elderly person and conspiracy. A third teenager was arrested Thursday. The youths’ names were not released because they are juveniles. Police told The Advocate of Stamford that on Feb. 11 the 15-year-old student picked up the man and slammed him to the ground, and three other teenagers punched him. Officials said the administrator had broken bones in his neck, back, and arm and was hospitalized until Monday.