I've played only three R&F games so far, but in all of them it appeared to me that golden ages are too easy to achieve. In the first game when my first two ages were golden, I decided to try and go for the achievement "3 golden ages in a row". In reality, ALL my ages were golden (5 or 6 in row, I don't remember anymore, and often with a huuuuuge overflow).
When I wanted to try the dark age in my second game, I had to actively go for it and then I got heroic and a row of golden ages.
The whole system feels a little bit weird to me. Normal ages are boring and in my experience hard to get, regardless the name "normal" (boring is ok, because "normal" means nothing special, but IMHO you also should get most ages normal and only sometimes a golden one or a dark one). Golden ages are not so good, because you pick one bonus and I mostly had to choose between something I didn't really need (religious boost) and something I didn't feel like getting much out of (a little bit better eurekas or inspirations). And dark ages? They sound nice, but I have so little experience with them (only ONE so far) that I cannot really decide. I, however, HATE the dark color scheme, there really should be a setting to turn it off.