To answer my own question:
from A_New_Dawn_GlobalDefines.xml
<!--Afforess:
How much Golden Ages lower the food requirement for city growth-->
<Define>
<DefineName>GOlDEN_AGE_PERCENT_LESS_FOOD_FOR_GROWTH</DefineName>
<iDefineIntVal>-25</iDefineIntVal>
So, in golden age cities require 25% less food to grow.
This looks very counterintuitive to me. In prehistoric era golden age affects city growth too much. For example, I have another 20 turns before my city will grow to size 2, now I've got Cave Dwelling and on next turn I will have size 2 city. On another hand, let's say I'm in golden age and there are 3 turns before city growth, golden age ends and here I am with another 30 turns to wait. I think that provokes unneeded and unintuitive micromanagement with counting turns to adjust golden age start.
I will remove that modifier in my games, but please tell me, what's reasoning behind it? May be it would be better to add some extra food every turn while in golden age? Then there will be no such huge leaps in number of turns for a city to grow when golden age starts or ends.
What do you think?
I think I rather like the reduced food needed to grow when in Golden Age. People are happy and thriving and are more apt to expand businesses with less resources at hand, taking a chance on the booming economy to expand and potentially gain more in the long run.
Besides it's a strategy game after all and one of the many things I plan ahead on when to do is when to enter a Golden Age. City Growth doesn't decide when I'll do so though, even if I do plan against growth for a city, or multiple ones, when I know a Golden Age is coming up soonish. I can even cap growth on cities that will grow before I enter a Golden Age, telling the populace that there is a ban on expanding businesses in the city for the time being.
City Growth factor is just an added bonus though, the main and always foremost reason for me to enter a Golden Age, and plan accordingly for, is Civic changes. I hold off entering a Golden Age until the same turn I get access to a civic I want to change to, and make sure that in the Golden Age allotted time I can reach several, depending on where on the tech tree I am, other important civic changes. If not I wait until I have a couple or more civics to change to and am able to reach the other nearby civic changes within the Golden Age.
Second most important factor is Wonders. If I've managed to get equal to, or even passed, the tech leader and I have a choice of at least one Wonder I deem important, possibly with some semi-important ones too, and possibly a few others lined up in nearby technologies, then I also enter a Golden Age to build them faster, hopefully fast enough to be first to having them built. This I also plan ahead for, knowing fully well when Wonder opportunities are on their way.
Third in line is Revolt Status. If it starts ramping up too fast, due to whatever, a Golden Age can very well save a Nation from total ruin.
When planning ahead for Golden Ages city growth just falls in line anyway as another part of the stratagem behind Golden Ages. Strategy is the main reason I play and enjoy Civilization and simply removing one part isn't in my best interest. I tend to bore too easily as it is already.
As for the weird sudden number changes until city growth;
During a Golden Age people want to be a part of the great economy and expand businesses, families, and so on, and move into cities to find their luck. Thus cities boom as well.
After a Golden Age ends people draw back, stop expanding, might move away from cities again, with the economic fall some even starve due to less income or even from having no work at all. Thus cities go into recline.
Cheers
