I don't know about you guys but I usually am not interested in joining a campaign in the that has been running for months already.
If it is an of-the-shelf campaign like Lost mines of Phandlever or Princes of the Apocalypse, I will have missed parts (and I cannot just replay that part later)
There is also a social aspect where a group develop their own conventions of inside jokes, plots and background. There is a risk that a new player will feel left-out.
So, I suggest a checkbox for "Only find New games" along with the selections for Free games, Mature games and P2P games
This will of course require that people do not post proxy-games to appear as new games. (probably not allowed already, but it needs to be enforced)
I am a but uncertain about the definition of a new game, but something like 3-4 sessions (times the frequency of the game).