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.
The pilot aired first on May 19, 2009 and the season started on September 9, 2009
8 to 9 PM on Tuesdays. However, Season Three will not start until fall of 2011.
The 3rd season of Glee starts in September 20th 2011.
November 9
September 9, 2009
Glee - 2009 Frenemies 5-9 was released on: USA: 25 February 2014
Glee - 2009 Frenemies 5-9 is rated/received certificates of: USA:TV-14
the fall of 2009