The latest info from Millennia gives us a lot of info about ages, but more importantly also information about the release: Millennia will be released on March 26 2024, and can already be pre-purchased. The standard version will cost 39.99€, and the deluxe version 59.99. The deluxe version will include two skins for early units, as well as two planned further expansions. You can pre-purchase the game here.
As mentioned, the latest update also gives us more insight into the content, as we now get small pieces of insights into each age. The “age of intolerance” for example will be focused on religion and how it shapes diplomacy and unrest in your civ, or the “age of aether” being a kind of steampunk age. For more information about all the ages please check this thread.