I mean MP game 1vs1. It is usually enough about 30 turns to surrender.
Really depends on the map then
For example, playing great land flat world, I've had games end by turn 25 (I forced a raze of 1 enemy settle and took another).
And then I've had games that went on for 65 turns or so before a surrender occurred.
And then on Saturday, we were playing a game that only reached turn 19, but we didn't even spot each other until turn 16-18 (and still haven't scouted the settles of the other player). The middle of the map was FULL of hills/mountains/swamps, and the main path that had a GFE and some other lair guardians.
It was clear that it would turn into a long 70 turn or so game, and my opponent decided he's rather stop since he did a UD rush strat, while I was econing up and had halberds out already.