The seven-man umpire crew working this World Series is easily the youngest in recent memory. It reflects the impact of computerized strike zones, plus other factors including injuries, retirements and postseason rotations. At an average age of 45.7 years old, the crew calling the Philadelphia Phillies-Houston Astros matchup is more than five years younger than the average of World Series crews over the past decade, The Associated Press tallied. So young, in fact, there won’t be a full-time regular-season crew chief on the field in Game 2 on Saturday night. Usually, two or sometimes three veteran chiefs are on the Fall Classic crew. The Series starts Friday night in Houston.