Ended then, but the earliest Indo-European speakers have been pushed back to around 6100 BCE, in Anatolia, and appear to have started spreading onto the steppes/central Asia well before bronze, let alone iron, was being used by any of the cultures involved.
The 'big' Indo-European spread, of course, was when the Yamnaya culture started moving into Europe after about 3000 BCE, a group which did use bronze - and spoked wheeled chariots and horseback riding, spreading the language group into the areas where it would progress into the modern European languages.
That migration also appears to have brought Bubonic Plague into Europe, which makes me wonder why the phrase:
"Aaaargh! I'm dying of the plague!"
isn't the same in all modern European languages . . .
What is all this hype around the plague about?
Btw, you nailed it with the Yamnaya culture perfectly. I couldn't have done better.
Anatolia and neighbouring cultures have an amazing depth in historical context about neolithic age.
The underground city complexes of Anatolia seems to have been linked amongst themselves consistently, and more and more
underground settlements keeps being discovered, revealing a huge network of cities in those areas.
In central Italy also the Etruscan *believed to be of a mix of native Italic, Aeolian, and Anatolian people, also have underground complexes
built in Ancient antiquity.
So what I'm suggesting, is to have some kind of alternative settlements for this age, to allow some kind of
gameplay that is not about building huge cities, but small settlements of some kind.
Rising sea levels would be also cool as Age ending event, or crisis, instead of generic plague...