Sgt_Kickaxe - 4:37 am on Feb 17, 2013 (gmt 0)
I just wanted to add that when you said "four years old" + "100 pages" I knew instantly that you got roughly 75-150 visitors a day. This seems to be a limit within Google and it takes a large number of incoming quality links and/or social mentions from high profile people to break that glass ceiling. In fact I know of at least two webmasters who build to roughly 100 pages and then move onto a new site because of how hard it is to get more than 150 visitors a day regularly from Google on a 100 page site.
Your next stop will be in the 300 page range with 400-600 visitors a day and you will know when you break into that zone because of a quick rise in traffic. Breaking that level is a lot harder, of course.
Maximizing ad revenue from existing traffic and increasing traffic are two separate monsters and you should be trying to do both.