First of all, here are the ages with precise years:
6000-6202: First Age
6203-6236: Black Age
6237-6312: Third Age
(What happened in Cycle 1? And before?)
Here are the Keepers of Avadon:
KEEPERS OF AVADON
1. 6240-6245 Telera of Dharam
2. 6247-6257 Herom of the Kva
3,4,5,6. 6257-? Diantha of Dharam; Geert; ???; ???
7. Redbeard
When was he elected?
6257? Nicodemus said. (1x reference) Then 55 years of service.
6265? It was written in the Codex (and 4x more reference, "he rules almost fifty years"). Then 47 years of service.
Redbeard must be from Kellemderiel, Dharam, or Tawon, because his childhood was on a farm, and these states are more civilised than the others, and he saw the remaining horrors of the Black Age.
5800? Corruption created
6000 First Age: the Pacts
6203 Black Age
? Redbeard born
6236 End of Black Age
6237 Third Age: The Treaty of the Five Powers signed
6240 Avadon created; first Keeper: Telera
? Redbeard's come of age (16,18,21 years old?)
6245 Telera poisoned, 2 year chaos
6247 second keeper: Herom of the Kva (obelisk in avadon: IN MEMORY OF HEROM OF THE KVA | FIRST KEEPER OF AVADON | [N], he died for you."??? The First Keeper was Telera! Or not?!)
6252? Redbeard arrived at Avadon ("must be sixty years ago")
6255 Herom goes powermad
6257 Herom disappeared, four more keepers: Diantha of Dharam; Geert; ???; ???
6257 Redbeard elected Keeper (by Nicodemus)
6262? Eye Leira enters service ("almost fifty years ago, almost as long as Redbeard")
6263 Lexrem of Dharam failed to poison Redbeard
6265 Redbeard elected keeper, almost 50 years (47) ago (Codex)
6272? Miranda's husband tries to kill Reedbeard ("about forty years ago") But when we meet her, she is described as in early fifties!? She was such a young wife???
6282 Heart Miranda enters service (she is only at Eye rank); Eye Leira rejects the plans killing Redbeard
6312 Current year
What is the canonic date of Redbeard's election?
I vote on 6265. The other date wasonly mentioned by Nicodemus, I think he inhalled to much alchemical potions! :-)