Calendar Fix
To relax the calendar... hmm. OK, we've got 500 turns to play with. In terms of advances to be discovered there are, what, effectively seven ages? Ancient, Classical, Medieval, Renaissance, Industrial, Modern, and 'Future,' where 'future' is the period where you're researching advances like Bionics that are cutting edge technology as of today in the 2005-2015 time scale- of which there are fewer than there are of techs in any of the other ages, so we can give it a bit less in the way of turns. And the game starts in 4000 BC and ends in 2050 AD. Right?
Our priorities are to have each 'age' begin and end at approximately the right historical date, AND to have each age take roughly the same length of time since this is History Rewritten!
(Stops newly inserted Greek leader from kicking a Persian worker unit into a pit

)
OK. To make it add up we need each of the first six ages to take about 75 turns, with roughly 50 left over for the final "Future" Age.
Now, on to the good stuff- the calendar. This is based on wanting 70-80 turns per age, and to have each age end roughly "as scheduled."
Thinking about it, and trying very hard to remember different parts of the world developing on different schedules in the pre-industrial period, when
should each age begin and end? "Classical" civilization (characterized by widespread use of iron working, literacy and the beginnings of philosophy, and increased trade and contact over distance scales of a thousand kilometers or so) can reasonably be said to have arisen some time around 1000-500 BC. "Medieval" times (characterized not just by the European dark ages, but also by the rise of Islam, advancing technology and the Chinese dynastic cycle in the Far East, et cetera) would arguably begin around 500-600 AD. The "Renaissance" (intercontinental sailing, gunpowder, and for most parts of the world the beginning of the colonial era one way or another) starts around 1400-1500 AD. The Industrial era definitely starts around 1750-1800, the Modern era around 1900-1920, and the "Future" Era around 2000-2020.
Let's go. [maths]
4000 BC: 50 years/turn (70 turns for the 'ancient' era)
500 BC: 15 years/turn (80 turns for the 'classical' era)
700 AD: 10 years/turn (70 turns for the 'medieval' era)
1400 AD: 5 years/turn (80 turns for the 'renaissance' era)
1800 AD: 2 years/turn (70 turns for the 'industrial' era)
1940 AD: 1 year/turn (90 turns for the 'modern' era)
2030 AD: 6 months/turn (40 turns for the 'future' era)
The progression stops being so regular at the end because I was running out of wiggle room.
Anyway, how does that sound? Wiggling the dates around gets tricky, but is doable, though I invite anyone who really wants it done to try it themselves.
Rate of Research
I submit that this "70-80 turns per era" figure should also act as your guideline for how long it should take to invent each technology and advance through each age, Xyth. Science production should roughly scale with the eras, so you can either tinker with the cost of advances or tinker with the available amount of research- but remember that this tinkering should extend to the ancient period as well; it does no good to tack on more tech buildings in the Industrial Age if it takes 400 of the game's 500 turns to
reach the Industrial Age.
So we'd need buildings coming online in the Ancient and Classical eras that meaningfully accelerate research, relative to the rate at which research normally takes place in those eras. I'll leave thoughts on that to other posts later on.
Or you could simply redefine the "normal" game to take more turns, which would also solve the problem well enough- I'd be happy to hear your opinion on that. If we need to adjust the game to take 750 turns to accommodate 750 turns of research, that's fine, and it creates a world that is in some ways more like the real world, in which by the end of the Iron Age in a given region there was very little of what might be called 'unclaimed wilderness' on the planet.