Weeding Magazines

Recently, I was told to begin weeding the Magazine Collection in the library. I was unsure on how far back to begin. I then researched the idea. http://olcsmalllibraries.wordpress.com/2009/05/04/weeding-library-c... I discovered that before the internet explosion, it was 5 years. Now, it is more like 2 years. Is this correct? I don't want to begin the weeding process until I am absolutely sure. It is a high school of only 300 students.