The stats of being, there are essentially four. The normal two known as life and death, then immortally and complete destruction. When someone is alive, their soul is tied to their bodies with a silver thread akin to an ambilocal cord, and when they die, that thread is severed and their souls ascend to the afterlife.
The conditions for someone's death differ, aging is merely that cord detreating through time, the more damaged it gets, the more the body gets shriveled and weakened until it reaches a point when the cord snaps and the person dies.
Complete destruction is when the soul itself gets destroyed and thus the person can't even exist in the afterlife as a soul.
The only way to make a god killable is to kill all of his believers and reduce him back into a demi-god that could be killed.
Gojo had become the first mortal of this age to kill a god. But the timer had ended, will he live with that achievement, or will it be his last and best feat?