I think the most reasonable thing to assume is that when it comes to matters of time, the Blizz quest and lore writers, independent novelists, are really out of tune. At best, they may try and come back to 'fix' mistakes that they have made in the time-line, but I think for the most part, it's just off. So, like the draenei who seem timeless, we too, should probably just not pay too much attention to it. The loose ends that make up Azeroth's history are fragile enough without people pulling on them. I think Brevus has the best idea: just keep it vague, or feign ignorance. Because it seems that's pretty close to the truth. "How old am I? I really couldn't say. Saying would be knowing, and since I do not know, I cannot say."