Just a heads up for anyone who cares; this new Age will go up in a few days on February 20th. Will probably cost between 20 to 28 million Gold and 2/3 weeks to build if you don't wanna spend Gems to rush it.
Will post more raw numbers when this goes Live!
Update: The nuclear has launched 12 hours early (or a day, depending on your timezone) and it only costs 14 million to upgrade!! Thank the devs for that, not the expected 25ish million. It takes 2 weeks to build, or you can rush it for 2000 Gems.