##Hard to tell: they've been around for thousands of years, and can stay alive for thousands of years

The in-game book *[The Dragon War][1]* tells us that that worship of dragons began in the Merethic Era (i.e. before the First Age, which began about 4700 years before Skyrim). The worship was brought by [Ysgramor][2], who was the chieftain that brought his people to Tamriel, the descendants of whom are modern day Nords.

> In the Merethic Era, when Ysgramor first set foot on Tamriel, his people brought with them a faith that worshipped animal gods. Certain scholars believe these primitive people actually worshipped the divines as we know them, just in the form of these totem animals. They deified the hawk, wolf, snake, moth, owl, whale, bear, fox, and the dragon. Every now and then you can stumble across the broken stone totems in the farther reaches of Skyrim.

> Foremost among all animals was the dragon. In the ancient nordic tongue it was drah-gkon. Occasionally the term dov-rha is used, but the language or derivation of that is not known. Using either name was forbidden to all except the dragon priests. Grand temples were built to honor the dragons and appease them. Many of them survive today as ancient ruins haunted by draugr and undead dragon priests.

So if this writing is accurate, then "dragon priests" were around for thousands of years.

As for "contemporaneous", that's a bit tricky because *[Amongst the Draugr][3]* indicates that the dragon priests are given unnaturally long life by siphoning off life force energy away from their servants.

> When the next group of draugr came to pay homage to the priest, I noted a sort of transferal [sic] happening. A distinct flow of life force between the adherents and the master.

> It was here that I finally understood the dragon cult's notion of resurrection. The second eternal life was only promised to those who ascended to the priesthood, but the lesser functionaries contributed their life force to sustaining them for eternity. I don't know what sort of eternal wellspring they draw from, but it's clear that each draugr carries only the barest whisper of life in it, and rekindles it nightly while resting in its niche. I now believe that the grotesque forms that we see in the barrows were, in fact, buried fully as men and women, and only over the thousands of years that have passed withered into the wretched things we know. If we had visited a barrow directly after its construction, we might not have even known any of its inhabitants were dead!

Given this, it's hard to tell if they are from various generations or if they are all from one generation. In-game they all seem to be in various states of decay, and given the latter passage saying that they might not even look dead initially, I'm inclined to think that they are all several thousand years old. Perhaps the older ones don't like sharing power with new upstart dragon priests.

  [1]: http://en.uesp.net/wiki/Lore:The_Dragon_War
  [2]: http://en.uesp.net/wiki/Lore:Ysgramor
  [3]: http://en.uesp.net/wiki/Lore:Amongst_the_Draugr