Board Thread:Naruto Discussions/@comment-1018594-20140824175144/@comment-1512913-20140824193222

The Hashirama-Tobirama-Hiruzen reign stuff also seem to have been retconned. The Sannin became Genin at 6, so supposedly Hiruzen began teaching them at their age, with himself having been 25.

Konoha is about 65 years old, but Hiruzen was already a Hokge just 16 years in the village's existence. So both Hashirama and Tobirama had at most 16 years together for their Hokage reigns.