Guys & Gals, you make something so simple into something hard
Start a Custom Single Player Game, Where it says Victory's, Uncheck all apart from Independance. Alacabam! Unlimited Game Time! Well atleast untill Someone Declares and Wins Indapendance......which at this point is pretty much impossible for the AI.
Uppign the Game Speed Just Adds hammars to production and makes everything else cost alot more(Units ect, Gold u get form treasure/Tribes)
I tried, have you tried? because It does not work so. You still have only 300 turns even if you uncheck time vistory. So, try it DCMage befrore you post.