It would most likely be because there are some theme's in the show that are inappropriate for younger children.
Glee season 4 starts Thursday, September 13th from 9:00 pm to 10:00 pm.
Glee shoes at 9/8c on Fox on Tuesdays.
It started on Monday 10th January 2011 at 9:00pm on E4
The first episode of Glee was ran on May 19th 2009.
8 to 9 PM on Tuesdays. However, Season Three will not start until fall of 2011.
The pilot aired first on May 19, 2009 and the season started on September 9, 2009
The 3rd season of Glee starts in September 20th 2011.
November 9
September 9, 2009
the fall of 2009
January 2011
in the fall