The golden age of hip hop was in the 90's, but the nascent of hip hop was in the 80's so I'd have to say we're probably somewhere along those lines right now for the UFC and MMA in general witnessing GSP, BJ, Chuck, Randy, Tito, Vitor, Wand, Mirko, Big Nog, Anderson Silva, and the progression into the next generation with JDS, Cain, Jose, JBJ, Erik Silva, Barboza, and many more.
I'd say 2000 - 2011ish was the golden age because that's when you saw quite a few MMA fighters retire; Chuck, Randy, Almeida, Lytle, Mirko, Frank Shamrock, Hardonk, Bas Rutten, Igor V., Pat Miletich, Royce Gracie, Rickson Gracie, Matt Hamill, BJ + Matt Hughes quite possibily and Brock Lesnar.
Probably missing quite a few more, but if you look at that list it's pretty surreal. More will be joining that list in the next several years. Once GSP and Anderson Silva retire that would be the definite close of the Golden Years if it isn't over already.
However the sport will live on and continue to grow through leaps and bounds.