Where can I set it so a civ starts in their Golden Age? I've looked through the Civilizations tab in Edit Rules, and through the Player Properties and don't see it. I know I've seen it before and it's kinda frustrating me. Thanks :)

I don't really know but Portugal starts in its golden Age in the Age of Discovery Conquest, because of a wonder creation I think. Might help you to analyze that.

Yeah, I looked in the AoD biq, and couldn't find anything about it, but wonder creation is an idea. Thanks for the help, does anyone else have any ideas on where it could be or how I could do this?

Wonders and units. In the editor select Starts Golden Age on the unit. Every time that unit has a victory, there is a chance for a Golden Age.

But how'd they get portugal to start in a Golden Age in the AoD conquest?

In the AOD conquest Portugal has just built the Dias Voyage wonder which starts their golden age.