Well... looking at the Character/World guide for FFIV, most of the nations in FFIV are relatively young. Baron is the oldest and it's roughly 500 years old. Mysidia was started around the same time by someone named Mihn on a fishing boat he captained, what is interesting to note about Mysidia's timeline is that Mihn is still active in Mysidia (now a Sage) 300 years after the founding of Mysidia, when Mihn gets angry at the humans misuse of magic and seals it along with Mt. Ordeals. Later "Mihn's Voice" would reawaken magic to help save Mysidia fifty years later, and afterwards, his voice will teach mages how to break some of the magic seals he placed on magic.
Now, Mihn could simply be two figures, the founder and then generations later a powerful Sage named after the village founder, or they could be the same person and possibly a Lunarian. I think the most likely evidence might be that Mihn is a captain of a ship that lands off the coast of where Mysidia was after a storm. Yet, Mysidia is also the location of the Lunar Whale. It's possible that Mihn was a Lunarian that first came to the Blue Planet before Kluya, it's not like Fusoya said that Kluya was the lone Lunarian to travel to the Blue Planet, and I'm sure it took a whole group of them to build Bab-il Tower, Kluya just might have been the last to visit the Planet to help spur humanity's evolution. Mihn also sealed all magic in the world, so it's possible that Kluya is simply just helping humans relearn magic by unsealing Mihn's seals. So if Mihn is the same person, it's likely Lunarian's have long lifespans, but its also possible that they have regular lifespans and its the Lunarians have just been taking turns on the Blue Planet between sleeping to help humans along. Course Fusoya doesn't have a confirmed age in the series...