post imperial age is when you have everything upgraded

Sorry, but you can't go from Imperial age to Post imperial age. When you start a random game you can start it in post imperial age though. I hope this was helpful!

Mongolia

No way to answer withot knowing the size and weight of the package, and WHERE in Mongolia it is going. You can check with the Post Office.

Under the empire period of ancient Rome, the Imperial Post were the official dispatches carried by special messengers. The dispatches were carried via carriages and also by changing horses at recognized posting houses. Private letters had to be entrusted to hired couriers or to friends making a journey, and only in special circumstances were permits issued to private individuals enabling them to use the Imperial Post.