The Iron Age can be researched at your Town Center, but the Post-Iron Age isn't a real age, it's just an extra setting on the map settings menu that starts you in the Iron Age with everything already researched.

It was a Gold, Silver, Bronze joke. :(

I got it. It is a good one :)

After the one where humans first harnessed water power, the Dam Age, and when we started wearing clothes, the Garb Age.

And carrying stuff, the Lug Age.

As well as dating in the Old Age.

At least it medaled. The same can't be said for the information age.