Board Thread:Naruto Discussions/@comment-25139119-20150923133911/@comment-25977287-20151005132821

When the konoha higher ups were debating whether Kakashi should become Hokage (just before the Kage summit arc), heir argument was that Kakashi was too young. Someone else then brought up the point that Minato was even younger. So I find it hard to believe that Hiruzen wasn't older than Minato or even Kakashi at the time he was appointed, because no one made mention of Hiruzen. The way Minato is talked about thoughout the manga, it sounds like he was the youngest to be appointed Hokage in konoha history.

Also something to take into consideration is that when Tobirama appointed Hiruzen Hokage, that does not mean he became Hokage straight away as soon as he got back. They may have waited a while. The databook certainly tells us Hiruzen was in his 40s at that time (whether it's a retcon or not, I don't care). The databook also states that Torifu was 30 at that time, so we can at least estimate that Hiruzen was of that same age group.