Okay,If you paid attention to the episode in Avatar LAB with the fortune teller and Katara wanted to know about her love life and all that. The lady told Katara she will die when her 4th grandchild arrives. Now..Tenzin's wife is prego with their 4th child....Can't wait to see if she was right.
Considering the fact that Tenzin is the youngest and he didn't get married and start having kids until much later in his life than is considered usual, it's possible that his older siblings could have grand kids by now making Katara a great grand mother. We'll have to wait and see how many, if any, great grand kids Katara has by now, and whether or not the story writers want to make that prediction correct.
Shes 86, which isn't extremely old. Pahtik was like 150, although he was a guru.
If Katara lives to 100, then Jinora will be like 24. Katara had Tenzin at 35, so if Katara lives to 111, and Jinora has her third child, then she'll die.
we don't know if Jinora is the oldest grand kid though. Tenzin has too older siblings, plus the fact that he waited until he was older to get marring and have kids (the man is in his fifties and his oldest child is only ten) it's possible his siblings could have kids who are much older and may even be grand parents themselves for all we know.
Since Kya and/or Bumi probably have older children than Tenzin does, it's really uncertain.
Besides, I have a theory that Aunt Wu's predictions influenced reality and not vice versa, so now that she's (presumably) dead, Katara's time of death may have nothing to do with her. emotion_c8