A common mistake. The GA - as so many other things - is about gaining turns, not about the total amount of extra shields/trade/food DURING the GA.
An early GA will gain those for you not just during, but also in all those turns AFTER the GA.
So, timing the Golden Age should be about when you can gain the most turns from it. In this month's game, a good time would be when the capital is building a Granary. If you can complete the Granary say 8 turns earlier thanks to the GA, you will leap turns ahead for the entire game (not quite 8, among other things because your Workers don't go faster during the GA, but still).
Another good time, still early, would be to use the GA to get to The Republic or Monarchy that many turns sooner.
On the contrary, BG's don't matter at all if the GA is under despotism.