Jabu Khanyile died on 2006-11-12.

Jabu Khanyile was born on 1957-02-28.

You have to be an adult, Most of the ground will be frozen and jabu-jabu will be gone. Just navigate the ice and make it to the cave.

I am not sure this is what you meant but to get into Jabu-Jabu you take a

fish and put it right in front of his mouth

You don't kill Jabu Jabu yourself. However, after seven years pass and you become Adult Link, where Jabu Jabu is in Zora's Fountain is replaced by ice. There's no explanation for his absence, although it's possible that Ganondorf may have killed him.