“If this was to be considered canon then Gwaihir would be exceptionally old by the time of his actions in the War of the Ring; at least 6000 years old.”
So what? Treebeard was alive in the First Age as well; and if one considers the Chapter Of Aulë and Yavanna in The Silmarillion, one will see that Ents and Eagles are of similar nature. Therefore, it seems quite plausible to me that Eagles have an extremely long life-span.
Furthermore, Christopher Tolkien explicitly stated that he considered it a mistake of his not to include the mention of Gwaihir and Landroval in The Silmarillion (in Sauron Defeated, chapter the Field of Kormallen). Canon states that on Tolkien Gateway, “[i]n general, The Silmarillion and Unfinished Tales are treated as canon, but corrections published in The History of Middle-earth generally take precedence.”
Greetings, 18.104.22.168 17:52, 3 June 2009 (UTC)