Htydjtk

In the Wheel of Time series, those with access to the One Power have extended longevity. At (roughly) 300 years old, Cadsuane Melaidhrin is believed to be the oldest living Aes Sedai during the series.

However, we also find in "A Crown of Swords" that there is

a large community of women called The Kin, and that some among their number are as old as 500 years.

Considering this, what non-Forsaken character in The Wheel of Time would be the oldest living user of the Power? I'm excluding anyone left over from the Age of Legends like the Forsaken, and when I say a user of the Power I mean a man or woman who channels. Also, I'm looking for the oldest still alive as of the end of A Memory of Light.

The oldest member of the Kin, and probably the oldest user of the One Power, is one Aloisia, who's nearly 600 years old:

“The oldest anywhere is a woman called Aloisia Nemosni, an oil merchant in Tear. Egwene, she’s nearly six ... hundred ... years ... old! When the Hall hears that, I wager they’ll be ready to put the Oath Rod on a shelf.”

“The Light knows three hundred years is a long time,” Elayne put in, “but I can’t say I’m happy myself at the prospect of perhaps cutting my life in half, Egwene. And what of the Oath Rod and your promise to the Kin? Reanne wants to be Aes Sedai, but what happens when she swears? What about Aloisia? Will she fall over dead? You can’t ask them to swear, not knowing.”

_{-- Winter's Heart, Chapter 10}

Then there's Lews Therin. Arguably he's still alive: his voice, memories, and knowledge are all present inside Rand's head, and sometimes Rand even starts to display some of his mannerisms and turns of phrase.

Reanne is the oldest women we meet at 412, however, she

dies

the next oldest in the kin that we know of is Sumeko Karistov who is speculated to be about 350-360, however, we have no proof of age only that shes older then, Kirstian who while not having a definitive age is at least 315, since she ran away 3 centuries ago from the white tower, and 15 being about as young as you come to the tower. So for known characters its between Reanne and Sumeko. Cadsuane is 295 years old according to this site wot where they say that in notes Jordan left it puts her attaining the shawl at 26 in 731.(current year being 1000 in Memory of light)

In terms of the oldest in this life, Aloisia Nemosni, as stated above is the oldest. However, in terms of rebirth, either one of the Heroes of the Horn, Rand or Mat Cauthon would be the oldest. The last is supported by Moiraine's comment while talking to Rand about his claim to the memories and knowledge of Lews Therin,

"You may have the memories of a man four centuries old, Rand al’Thor, but that does not make you ancient. Otherwise, Matrim Cauthon would be the patriarch of us all.”

_{The Wheel of Time: A Memory of Light}