Me I just arrived at it in the year 1776. The remaining civs are advanced to my current enemy comes at me with marines and the 2 remaining peaceful civs have bombers. I got a spy in every capital.
I think this largely depends on Settings, Map size, # of civs and whether you have pangea or not.
I usually end up at the Modern ages in the 1700/1800 if i ever make it that far.
it depends on the level of the AI. On regent and up, the AI will research faster, making the whole pace of the game much faster... Play a game on deity, and you'll be surprised of the date you'll reache the modern times (if you ever survive!)