Is Aragorn half elf? i seem to remember from the third book that he lived to be like 170.

Aragorn was high king because he was a direct descendant of the Númenóreans, the men who were friends of the elves in Valinor. The elves created the giant island of Númenór for their allies, and the Men created a vast and powerful kingdom there. There was much interchange between Númenórean men and elves then, and some of the Númenórean leaders were half-elven. By stint of their long association (as well as sharing some blood), the race of Númenórean men became somewhat magic: exceptionally strong and long-lived. Númenór was destroyed and the survivors formed the kingdoms of the Dúnedain in Middle-earth, Gondor and Arnor. Though much time passed, the pureblood Dúnedain (Númenóreans) still had longer lifespans than other Dúnedain, much less normal men. Aragorn claimed to be the last of the Númenóreans.

Nope, he was just raised by elves after his parents died. He lived to such an old age because the Duneadia, whom he is part of, are blessed with long life.

NO he has unarural long life because the guy you had the ring first (his ancestor) lived longer because of the ring and it kind of passed on through the blood.

he was of the race of the old kings the dunedian which weree the kings of the nuemonor. aragorn was astraight desendent of these great people and they live for a long time