Sorry guys still haven't got around to doing some proper rules for this (if you wait another couple of weeks I'll be done with all my asisgnments for the semester and can devote some time to it >_>).
I wouldn't set milestones by year. The rules for spreading dudes around will have a set level of cultural technology which triggers the next "age" and each turn will last a set amount of time, so the first city will be founded when people are advanced enough to found it, which may be sooner or later than it was historically on our world.