While Im aware there is no real pin point in time we can say each of the city states was founded, I was idly curious as to the rough times the current city states was founded, if anyone has any real idea.

Gridania seems to be the youngest, born of Gelmorra some five hundred years past.

Sil'Dih was founded at the same as Ul'Dah and by accounts was smaller.

Ishgard, and I have no real evidence to prop this, seems to be the oldest by thefurther dating of events attributed to the city, aka the dravanian war length.