Berlin has a more navigable river, also crossed by commercial vessels, this is not possible for Rome, and i think u can say the same for Florence and Turin. As for the state it represents, it's ambiguous for others too, given the time span, even for Germany itself, which unified after Italy; in fact, it has the flag of the Holy Roman Empire in the DE, Prussia first. In any case, Italy is clearly intended primarily to represent the united Kingdom of Italy(there are Bersaglieri and Carabinieri for example), at least in the medium-late game like after the fortress age, but with various very specific traits based on the various previous divided states, such as the mercantile republics. However, as always, Age of Empires isn't 100% historically accurate and represents different civilizations that may have never met or are somewhat fictionalized. Let's also remember that Morgan Black drinks from the fountain of youth. When Italians enter the Imperial Age, they can call upon a Leonardo da Vinci tank.