From YYH and Japanese words defined:

jiji = old man (disrespectful), old geezer. Fuji Shinichi's Hiei routinely calls Koenma 'jiji' (despite his appearance Koenma is hundreds of years old). Even worse than jiji is 'kusojiji' which is difficult to render in English. 'Old fart' is about as close as we can get, but it's really worse than that.

Also a note: We think Fuji is mistaken about Kurama's age here (this is one of her early works). Our best info is that Kurama is a four-tailed fox. ^_^   But he's still pretty old.