the 12-Year-War culminated in 515 A.D., if I remember correctly, when Grendel’s arm was torn off by Beowulf;  meaning that it started in 503 A.D.  Grendel was born in the year 343, so  –  he was 172 years old when he died;  160 years old when the war started.  As of 2020, he’s 1,677 years old.

this may seem super, like, You Were Almost Two Centuries Old Dude What The Fuck, but ceti don’t age like humans do;  for Grendel, 160 was adolescence.  he was basically just a 15 year old idiot kid.