I see it like this:

The Bronze Age:
FFI
FFII
FFIII

Things were just getting started, the series was finding its metal to forge things out of, but it was still a harsh time, the games were still a little rough around the edges...

The Golden Age:

FFIV
FFV
FFVI

For most RPG fans, the 16-bit era will always be this magical time when the genre found its mark and what made it really great was established. I think it deserves the golden age title because it is a very nostalgic time when things seemed simpler.

The Platinum Age

FFVII
FFTactics
FFVIII
FFIX

I'm using this because I think the PlayStation One era was a time when games that exceeded everything we thought possible were taking place. The titles coming out were more valuable than gold. Whether it's FFTactics or Xenogears, there's probably a game in this era that takes all the categories up to 11 for you. FFVII felt like the game I was waiting for all throughout the 16-bit era. Others felt IX was a stunning return to the series roots. And then we have the few who thought VIII was the best in the series. I designate the PSOne as the Platinum Age of RPGs.

The Gilded Age

FFX
FFXI
FFX-2
FFXII

If you haven't heard this term in US History, it means everything looked golden but that was just skin deep; underneath was a cheaper material simply painted over. Now FFX and XII are two of my favorite games of all time, but this is where the problems started (and The Gilded Age saw the beginning of some of the problems that led to the Great Depression). We had some really, really shiny graphics making games look better than ever before, but the magic started slipping away. FFX had its linearity hidden beneath its gorgeous exterior. And while FFXII is in my top 10 RPGs, I still think it didn't have that FF magic feeling that earlier entries had.

The Dark Ages

FFXIII
FFXIV
FFXIII-2

Just like Europe receded back from great empires and kingdoms to local, local, local villages, this was when the great RPG genre was broken and developers began running to hide on handhelds. Mainstream publications are made up of journalists who question if JRPGs really ever were good to begin with, claiming that things like turn-based combat, linear progression, and cutscenes are, inherently, by virtue of themselves, bad game mechanics. Just like the Holy Roman Empire wasn't holy, wasn't Roman, and wasn't an empire, FFXIII doesn't hold up especially well to the great legacy of Final Fantasy. It's hard to tell where the series and genre can go from here, such a low point...

Let's all hope for a renaissance