I have to agree, 1500 doesn't seem old enough. I'm having trouble remembering which book this is in, so if anyone knows, help me out here. I'm fairly certain that it's in 'Salamander', but again not sure. All I remember is that they find a space marine locked behind a door, and that he had been sitting there since just after the heresy. He was the last of his squad alive, and had been sitting there keeping watch over their armor, with the memories of the battle that had slowly killed them off over time. He finally dies in the book, but not before passing on the precious information to the Space marine that finds him. Should no one be able to think of this, I'll site it once I get back home (Away on business currently). That being said, I would think that this should be a good base line for how long a normal SM can live before dying of old age. Primarchs, I would assume, would live well beyond this age. Again, apologize for being so vague.
Yep, that's Salamander
. Though it implies that the Marine was also vegetative for the bulk of that time and perhaps in a sus-an-membrance trance.
Anyway, with regard to the topic: I like the idea. It's certainly speculated that Vulkan could survive. When I read Hammer of Daemons
(and it's a fine book, easily the best of that trilogy) my mind did leap immediately to Vulkan.
Of course, it could be anyone. Any Space Marine who's been in the Eye of Terror long enough could start looking like that. He could be an oddball Iron Hand, a loner Iron Warrior, he could be the last Space Marine, still alive but in the past millions of years after seeing the end of everything, but alive in the Eye knowing how to sort things at the right time.
I like the Vulkan idea, but Vulkan is a huge well of possibilities, but it's also easy to see him everywhere, hiding in every bush and behind every conspiracy. Kudos to the OP, neat conjecture.
Bear in mind: the Primarchs are not Space Marines. They're the genetic forebears, but they're not Space Marines
. They're a different breed of super-human. They're varied, there wasn't an exact cookie cutter for them (as we learn in Deliverance Lost
- the Emperor valued variation).
It's possible that some have innate bits about them that make them live longer/shorter. Perhaps Ferrus Manus and Sanguinius were capable
of immortality...but Dorn and Vulkan were very much destined to die. Perhaps Alpharius is nigh unkillable? (A literal head of a legendary hydra: cut him down, two more sprout up!)
The thing is, for all we know of Space Marines, we know almost nothing of the Primarchs. Fabius and such remark on precisely this in the Heresy books. Talos and Variel (IIRC) muse on it in the NL books - they really are wondrous, unique creatures. Even with twenty of them, there's no telling quite what they were capable of and what their limitations are.