But First You'll Need To See This...
During the Fellowship of the Ring, Aragorn (played by Viggo Mortensen) is already 87 years old. Arwen his seemingly on-and-off girlfriend and of course his wife-to-be (played by Liv Tyler ) is actually a distant cousin...by a few thousand years. Arwen and Aragorn first meet when he is in his 20s and she is just over 2,700 years old...give or take a few years.
THE ELVISH CONNECTION
Elrond, Arwen's father who is (played by Hugo Weaving) is over 6000 years old. He and his twin brother Elros are Peredhil - half elven. After the War of Wraith, (a battle against Sauron's master Morgoth) the twins were the only descendants left from the heroic chieftain line - the line of men that stems from the first age.
It was also after the War of Wraith that Elros and Elrond were given the choice of two new fates for themselves. The options for their destinies lied in 2 paths, where they were offered, by the Valar; 14 angelic super beings (well 15 but Melkor became Morgoth) to pick from either having a human or elvish fates.
Elros chose to remain with within the line of men and became the first King of Numenor and though not immortal, his reign lasted 410 years. Whereas Elrond chose an elvish existence and became the captain of Lindon and herald for Gil-galad, with an immortal spirit hence his age ancient age.
Continuing with the Elvish connection, Elrond's mother-in-law is Galdriel, one of the most powerful Elves in LOTR lore. She is married to Celeborn and Elrond is married to their daughter Celebrian. This means that Arwen's grandmother is Galadriel.
Aragorn is a direct descendant of Elros hence his young looking face, but considerable age. It is because of his elvish ancestry that Aragorn has a longer life span than the average human being. In his early days, Aragorn assumed the rank of the 16th Cheiftan of Dunedane - to The Rangers of the North and it is around this time that Aragorn first met Gandalf the Grey. It is also at this time when Aragorn performed a lot of services for the then King of Rohan - Thengal. King Thengal is Theoden's father later seen in The Two Towers, Aragorn is actually 17 years older than King Theoden.
THE FALL OF MORGOTH
Having made an attempt at world domination and failing, it was almost 500 years later, of laying dormant, before Sauron made steps to come back for a second attempt. This time around he was the dark lord, as his previous master Morgoth, had his own brother Eonwe (who was still a Valar) cast his spirit beyond the Walls of the Night - into the void.
Sauron now began to pitch his own bid to take over the Earth, first seen in The Hobbit films and especially in The Battle of the Five Armies, where Sauron had already given the 9 human kings their own rings of power.
Upon Sauron's defeat at the end of The Return of the King, Aragorn was named Elessar Telcontar, by Galadriel, meaning Elfstone Strider. And upon his coronation he became the 26th King of Arnor, the 35th King of Gondor and the 1st High King of the Reunited Kingdom. Aragorn goes on to live until 210 years of age staying married to his royal queen Arwen for 122 years. In Aragorn's passing, Arwen, due to her broken heart, joined him the following year, leaving their son Eldarion to rule as the 2nd king of the Reunited Kingdom.
Bring on the Silmarillion!