Dog Knows what criteria ChatGP was using, but when I looked into it some time ago there are at least three different 'systems' of dividing human existence into periods: technological, historiographical, general - and that's leaving out older 'systems' like Greek Mythological.
And before you ask, none of them match. Just about the only thing they all agree on is that 'Neolithic' is the last part of the 'stone age'. After that, you takes your pick.
The game designers took their pick, and they are neither wrong nor right, just one option out of a number of options that the professional historians can't agree on either.
I agree with
@Evie, though, that the problem is not with the in-game Ages themselves, but with the transition periods, that hide the equivalent of another Age of time in a Black Hole of events which are presented to the gamer at the beginning of the next Age. The gamer's only input into these events is how he/she ended the last Age: no allowance is made for modifying the future of your Civ by navigating the 'transition' (or Hidden Age) in a different way.
Now, this is a problem, because one of the purposes of the Age transition is to present the gamer with a largely new Civ to play (with only some Obsolete or Ageless buildings in his settlements, some Legacy bonuses carried over from how well the last Age ended, and some units magically 'upgraded' to the new age but also scattered hither and yon in your territory - sometimes infuriatingly so) and the opposition 'reset' so that the proverbial run-away endgame is/should be Impossible.
It isn't, of course: I just started a Modern Age with approximately twice the Science and Culture per turn of any of my AI opponents and twice the settlements, which is close enough to 'run-away' for my book. But any modification to the transitions allowing the gamer more input risks negating the transition effect on game imbalance even more, and puts Civ VII on the same track as previous games when the whole game system was designed to try to avoid that.
Because the one absolutely certain fact is that the AI will not be able to 'game' the transition as well as the human player, so making the transition period a playable sub-Age will inevitably increase the potential imbalance between human and AI as the game progresses - a problem that every long-term game (Civ, EU, etc) faces.