FFII - 5 years
FFIV - 5 years
FFV - 5 years
FFVI - Over a decade
FFVII - 5-6 years
FFVIII - 4 years
FFIX - 6+ years
FFX - 1.5-2 years
FFXII - 7-8+ years
FFXIII - Since it's release
FFXIV - Last week