At the age of 210, on March 1, 1541 (FA 120), Aragorn resigned life, as his son, Eldarion, takes his place as King of Gondor and Arnor – and recalls his final words to his wife, Arwen:
“Lady Undómiel,…the hour is indeed hard, yet it was made even in that day when we met under the white birches in the garden of Elrond where none now walk. And on the hill of Cerin Amroth when we forsook both the Shadow and the Twilight this doom we accepted. Take counsel with yourself, beloved, and ask whether you would indeed have me wait until I wither and fall from my high seat unnamed and witless. Nay, lady, I am the last of the Númenóreans and the latest King of the Elder Days; and to me has been given not only a span thrice that of Men of Middle-earth, but also the grace to go at my will, and give back the gift. Now, therefore, I will sleep.”(LOTR, App. A)
This also would be assumed to mark the fall of Rivendell. Aragorn seems to have been given the gift, or doom, of death however one views it – that the early Numenoreans had and chose the time of his passing. Had he not chosen the time it would have occurred soon, and eventually.
What made Tolkien write Aragorn’s end like this?
Tolkien had Aragorn die in this manner the way the other Numenoreans did – including Elros Tar-Minyatur who would die willingly when he did.
“The doom of the Elves is to be immortal, to love the beauty of the world, to bring it full glower with their gifts of delicacy and perfection, to last while it lasts, never leaving it even when ‘slain,’ but returning – and yet, when the Followers come, to teach them, and make way for them, to ‘fade’ as the Followers grow and absorb the life from which both proceed. The Doom (or the Gift) of Men is mortality, freedom from the circles of the world. Since the point of view of the whole cycle is the Elvish, mortality is not explained mythically: it is a mystery of God of which no more is known than that ‘what God has purposed for Men is hidden’: a grief and an envy to the immortal Elves.”(JRR Tolkien, Letter # 131)
This grief and envy would occur to some of the preceding Numenoreans, who desired immortality that they would attempt to get there through rebellion. But Tolkien must’ve written Aragorn that way based on how the early Númenóreans lived and experienced life.
It is commonly thought that Aragorn died because he didn’t want to be remembered as an older man. While it seems he chose to die before becoming senile, Aragorn will be 210 years – though in the first draft, he would be 190 years old, when he resigns life – which would make him well within his aging period of life.
‘When Aragorn resigned life at 4A 120 [he resigned] 24 years of life. He had lived 210 years and was already within his “decline.” Arwen was reckoned as 203 years at that time and also in the beginning of her decline. Aragorn resigned on the day of his birth, March 1, 4A, 120. Arwen apparently “resigned” life and died on Cerin Amroth on March 1 in the following year, at Númenórean age 204 (mortal equivalent = 84). So she was now and felt.”(NoME, “Elvish Ages & Númenórean”)
“…it seems probable that Aragorn’s life was similarly arranged: thus he grew to maturity as quick as the normal human rate, and then slowed to the Númenórean ageing rate of 3:1. He was thus 20 in 2951; but [in 2980 about 30 and at wedding nearly 43, close in age to Arwen] and at death [he would be nearly 77.”(NoME, “Elvish Ages & Númenórean”)
If this is the case, much like his wife, Aragorn would also join a different expectation of life following the wedding – though he was always in the line of the Númenóreans.