This graph shows the age of rulers of Men throughout the history of Middle-Earth. The life span of Men is claimed to have shortened over the years.
It is explicitly stated by Tolkien that the longevity of Men once granted to the Númenóreans decreased over the years. In Letter 156 Tolkien writes that "a good Númenórean died of free will when he felt it be the time to do so". With the Shadow and the Downfall of Númenor this grace was taken away from them and they died involuntarily with a decreasing lifespan.
The decreasing life span is seen clearly in the graph. The most dramatic change is shortly before the Downfall of Númenor. The rulers are shown in order. Their number should not be confused with how many generations from Elros Aragorn is since there were more than one line of rulers.
The last bar represents Aragorn and you may notice it is noticeably higher than many of his ancestors. In The Tale of Aragorn and Arwen it says: "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." This explains Aragorn's long life.