First off, there's no way to manage the different time spans between turns, you could cylce the beginning turn in a .sav game and use that as the beginning point for your mod.
As for not advancing to the different ages, you can just rename the ages using the editor. You could name them after the various periods the Romans went through. Then re-work the tech tree to fit these different eras, and rework the icons and buildings/wonders/units to fit these periods in time.
Other than that though, there's not much else you can do to stop the game from advancing eras. The only other solutions are the already proposed increase tech costs to 1000 in the ancient era and jack up the maximum time to get a tech. But even then that would only be about 1/5th of a game, and that's without taking into account the 60% reduction the AI would get at the highest level to its research cost.
You could also place lots of buffer techs in the Ancient Era and set them up like "future techs" so as to stall the advancement to another era. But I think the most elegant solution would be to rename the eras and rework the tech tree; of course this would be the most time-consuming option.