User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-1758220-20130402064114

If the village chief's stories are any indication, the Lagiacrus (or at least the Ivory species) live considerably long lives.

He doesn't explicitly state this about the monster, but he seems to imply that the Ivory Lagiacrus you are preparing to fight is the very same one he fought over and over again unsuccessfully as a young man.

Now I'm going to go out on a limb here and suggest that the Moga chief is quite old, I'd say late 70's, early 80's. He must have been mid-late 20's in his prime as a hunter, and by then the Lagiacrus sounds like it was already fully grown.

TL;DR: Lagiacrus can live at least past the age of 80.