en_tn/1ki/02/06.md

do not let his gray head go down to Sheol in peace

Here being old is represented by having gray hair, that is, a "gray head." Alternate translation: "make sure Joab dies a violent death before he grows old" (See: rc://en/ta/man/jit/figs-metonymy)

Sheol

the grave or the world of the dead