saving his life after a coup by his advisers.
During the quest to do so, players witness the following exchange between Rezan (Loa of Kings) and Bwonsamdi (Loa of Death):
Rezan: The Little King will rise. I am not finished with him. Bwonsamdi!
Bwonsamdi: Ya got a bellow dat would wake da dead! What ya want, mon?
Rezan: You have taken what is mine. Release him.
Bwonsamdi: Long time, ya been keepin' dis one from me. Long, long time. I'll be denied no further.
Rezan: Know your place, loa of graves, or I will put you in one.
Bwonsamdi: Comes a time when we all gotta die... even kings.
This conversation seems to imply that Rastakhan is much older than other trolls, which typically have a lifespan comparable to that of humans & orcs. Or perhaps that he has escaped death on multiple occasions. Howeverm the "long, long time" bit leads me to think that his lifespan has been unnaturally prolonged by Rezan.
How old was King Rastakhan at the time of Battle for Azeroth?
Note: I am asking here instead of Arqade SE because this is more about the game lore than gameplay or mechanics.