Nice introduction, Novice.
First the revolt into caste. Well, that was a gimme. This golden age is for our protection - we are permanently entering nationhood, and accelerating Rifling as well as Steel-Railroad-Combustion. Leaving slavery doesn't hurt us much because nothing we can whip will make much difference compared to drafting, especially drafting rifles. And caste system lets us get rifling sooner, so, it's in.
Second, the war declaration. Here is a picture of the theater of war. You can't see much that clearly but all you need to know is Mackoti has a big army where it looks like he has a big army, namely in his gems city and 1N of it. What you don't see is a Sumerian worker adjacent to Poetic Moss building a road. The reason for this is that we declared war, used two knights to take out the mace and knight that were guarding it, and deleted the victor along with the worker. This did two things:
1) Mackoti can't attack Poetic Moss for an extra turn. In that extra turn we will at the very least draft another musket and we also threaten to raze vopsitoria (his coastal jungle city) with our own knights. Every turn we delay his knights is a big win because he will have to tech MT and upgrade them to cavalry for them to do anything vs riflemen.
2) We got a great general. Not sure what we will do with it but it's sure nice to have.
The knight that killed the mace in fact got lucky (winning a 34%ish battle) and now has 12xp, so we can build the Heroic Epic now regardless of what we do with the general.
So basically the answer is we were already all but at war by his hand.
Friendlier matters: with the golden age popped there are 3 cities that got careful calculation, the ones that will produce a great person during it. No other cities could get near.
Attach Mimes is scheduled to pop first even though it had the fewest gpp going into the golden age. The reason is that neither of the others are expected to ever produce another great person, but AM is, so we want it to get as big a head start on the next one as possible. Luckily AM is first in city order so it's relatively easy to make it pop first. It's just going to run specs down to 0f over the next 5t, pretty easy.
BY also turns out to be easy. Similar philosophy and it pops the turn after AM.
ES was a hard one to get right - basically I had to either let it go first (which was bad) or it had to lose a pop. So I went with plan C and am making it lose 2 pop. Why? Well instead of filling the food box I just let it grow an extra size right before the golden age, and it turns out to be more efficient this way. Plus it has several nearby cities which can borrow its food resources while it's starving, so that's a fantastic bonus.
The best part of this though was that to pop out the third GP, ES has to run an ungodly number of merchants. And guess what? Due to taking its time, having just half a food bar to run out over three turns, I was able to work a bunch of hammers this turn and finish its grocer. It was close enough that before ending turn, the interface said the grocer was due in 2t. But hey, that's a windmill there, and it got +1h when we teched Replaceable Parts, and what do you know, tech happens before production.