How long does the Golden Age started by Taj Mahal in Civ5 last?
Solution 1:
The base number of turn for the Taj Mahal is 15 a turn Golden Age. The Chichen Itza world wonder will increase that number by 50% (= 22 turns).
Building the Taj Mahal as Darius resulted in a Golden Age of 33 turns (should only be 50% longer). Darius with Chichen Itza resulted in a 49 turn Golden Age.
The base value seems reasonably balanced to me, maybe a bit too powerful. With Chichen Itza it is very powerful, but Taj Mahal with Darius is just outright overpowered, or even broken.