If you're talking about barb cities, yes the condition is 2 per civ on average.Note, that if Alex can't build a 2nd city, then barbs won't appear till Qin or we settle another, right?
Alex should be able to build a second city. Athens is only size 2, so he is building a settler (or has a really lousy location; does anybody know if Gyathaar hates Alex

And the CIV AI does not build a settler if no settling location is possible (in contrast to civ3).