Hey I have no idea about what KW density is best or if there is a "best". But the first time I submitted pages to inktomi one of them showed up #2 for its keyword - so I doubt that time in the DB has anything to do with ranking.
Besides if that was the case a lot of old crappy site would all be #1
In the past Inktomi had a rather old database, called BOW (Best of the Web), that gave some kind of boost to sites (most rather old) in it. It has been dropped once they started their current spidering of the whole web, see [webmasterworld.com...]