Sigh.
I'm torn between all three Ages.
I did my graduate work on the Hellenistic/Alexandrian period of classical history, and I've always loved the 'blank map' feel of the early game - seeing and finding everything for the first time is a thrill that never fades.
BUT
I also spent years researching the late 17th - 18th century and have recently been reading a lot of new books on medieval British and French history. As much as any other period in human history, this is when men's eyes got opened to new ways of doing things socially, politically, militarily and culturally
BUT
For the past 15 years I've been doing archival research into aspects of the 20th century, and I've lived through enough of modern history to be intrigued by how the game will handle it - from Robber Barons o the 19th century to Tyrants of the 20th and people's reactions to them - Progressive, Regressive, Fascist and Anti-Fa, Commie and Capitalist Pigs (funny how the same animal is used to malign two supposedly different groups).
Mostly, I'm hoping the game succeeds in its stated purpose of keeping the last Age as interesting as the first. If they do, this will be the first Civ since IV that I play as much of the last 150 turns as I do of the first 150, instead of the ratio being about 10 to 1 in favor of the early game, as it has been in Civ VI . . .