Near 2012, you could read articles and story. Long long long time ago, God creates 4 different Ages. Golden, Silver, Bronze, Heroic, Iron ….Age of Man

 https://en.wikipedia.org/wiki/Ages_of_Man

I don’t remember it was this story. It’s a Greek mythology ?

Sailor Moon is Silver Millenuim. 

Magazine SMCH count dates after certain years pass 2000, they use Golden year

Under what’s 銀千年 silver crystal?

https://youtu.be/3BuFAVLzI0w