Thank you all for the helpful pointers. I'm shocked! It turns out they are running Windows Server 2003 32 bit and no one ever configured AWE, PAE, Locked pages, etc. Windows never gave more than 2 GB to sql server 2005 so it ignored my min server memory setting. The Page Life Expectancy was always under 200 sec. They never used 12 of the 16 GB on the server.

I was misinformed about the 5 minute aging. Turns out that is an old rule of thumb of at least how long a page should last.