This is a minorish sort of spoiler for upcoming episodes.
It has full baring on this topic and might help put to some light theories going on on here in this thread.
This isn't to to huge or anything, but if you want to be kept totally in the dark about Jacob and the MIB then don't click.
It's basically exactly what the writers and the characters have been saying so far this season without all of the fan speculation and attempts to tie in things and make things bigger then they already are.
In an up coming ep. we will see Jacob and the MIB as young children when they first came to the island. Apparently we will also see one of their mothers.
So neither (or both) of them are Aaron or any other character we've seen or met so far. They are themselves. Once real, normal people. Who came to the Island when the were very young. And stayed.
Apparently something like 62A.D. so at this time they have been on the island for something like 1945 years.
This is also interesting in that it puts them there after all of the Egyptian stuff that was built on the Island, since the height of the Egyptian Empire was still several thousand years before that.
Interesting information, I look forward to learning more about this