Geb broke the world record on what, marathon 7 and 9? Number 9 was also 15 years after his first world champs win as a senior (2008 after a '93 WC win). Kipchoge has lots of time (maybe even wait until next year, '18 after '03).
He also ran 2:03:05 in London, which is not usually seen as a world record course, he took over a minute off the course record to get it down to that. Olympics was a tactical win, no one was going for a record that day. Kipchoge also ran 2:04:00 in Berlin with his insoles falling out. I mean sure he never ran the world record but he clearly has had some reasons for not getting it.