Most strategy games will have some kind of snowballing. I had this exact problem also in civ. 

Even on the highest difficulties and slower speeds I scale way too fast. After medieval era I can usually just blast through the next eras so fast I don't even get the chance to use any units before they are "out of date".  The problem is when I start scaling I earn way too many era stars. 

I think there should be extra settings so I can change how easy it is to earn the era stars.