The Architect,
I did forget the Kreia mentioned that Reven had a mother and father, but i don't think that really sets and origin in stone anyway. Kreia could be lying, does not know, or they could be surrogate parents.
According to what i read, the true sith existed before the Ajunata pall/ tulak hord/ marka ragnos era of sith. "According to Kreia, the "True Sith" had existed for millennia prior to the rise of the ancient Sith Empire." (From True Sith page on wookieepedia) This coincides with what i wrote in my first post.
As for the age thing, from what i have researched, the mandalorian wars took place between 3976-3960 BBY and the Jedi Civil war was between 3959-3956 BBY. Lets assume Reven left for the unknown regions in 3955 BBY. Reven joined the Mandalorian wars after they had started and being that he is a normal human (ie. aging) i figured that at the age of his 20s he could conceivably be ready to take on such a task. Therefore it would likely make reven in his 40s when he left for the unknown regions. So through a little research i have found that reven must have been born in 4000 BBY give or take five years.
My first thoughts were that the game can't go into the unknown regions because that would require the team to develop too much star wars canon about what was in the unknown regions. however, after research i realize that there is already a lot in canon talking about what lies within the unknown regions. so therefore i think it would be exciting to venture into this fairly unexplored world.
as for the characters you play, i do not think we can play as reven or the exile in kotor 3 (or at least should not) because it would interfere with every single player's idea of who reven is exactly. as a matter of fact, i'm not even sure if we should find reven or the exile. if there is an npc of reven people would complain what he looks like, what his powers are etc. same with the exile. and it wouldn't make the game very interesting if we started out as an immensly powerful jedi who didn't have to worry about building his skills (ie leveling)
This is why i think a third character is necessary. I've read various ideas, but very few of them ammount to the same level of story telling that these games have provided. This third character must already have ties to the story somehow. Maybe they were the padawan of somebody important and they never finished their training (they could have trained at the enclave on dantooine or at the sith academy on korriban, not really important but it gives you the lightside/dark side origin choice like you had in kotor 2). possibly your master brought you away from the mandalorian and jedi civil wars becuase he knew what it would do to the galaxy and he trains you as a gray jedi on some remote planet (i think a nod to dagobah would be kind of cool since you could explore the world a little bit more than the movies did). maybe you are even the son/ daughter of bastila and reven and you are off to find what happened to your father. (this would avoid the problem that i have with actually encountering reven as an npc since it's possible he died years before you were ready to begin your search.)