The 3rd was trained by the 1st and 2nd. Remember the picture of him as a kid with them.
I think he was asking if Iruka even met the first and second hokages. To which the answer would be no, and Iruka was a little kid when the fourth made a name for himself so he wouldn't have known much about him either.
The only thing that anyone with any credibility has said is Kabuto who said that he was the strongest of the 5 kages of his time, meaning stronger than the 3rd tsuchikage, raikage, mizukage, kazekage. Which personally I think is a load of BS because let's take a look at the 3rd kages and compare them to Hiruzen.
Onoki 3rd tsuchikage - Dust release, can fly, earth element, basically whatever Muu can do, is much older than Hiruzen was at death and has way more chakra then Hiruzen and is still an awesome shinobi.
3rd raikage-unable to be hurt except by himself, faster than Hiruzen can possibly be, stronger, much more chakra, this is a fight Hiruzen cannot win.
3rd Kazekage - said to be the strongest kazekage, magnetism release, that sort of thing.
3rd Mizukage - we know nothing about the 3rd Mizukage as far as I am aware but considering his peers he should be extremely strong.
and finally
Hiruzen Sarutobi, 3rd Hokage - had knowledge about every jutsu in Konoha, (he wasn't able to use every jutsu in Konoha though), master of the 3 basic ninja skills, Enma summon, no special abilities like the other hokages, we was more the classic shinobi.
In my opinion, Hiruzen would lose to the third raikage, and Onoki. I think he could probably beat the third kazekage and we know nothing about the 3rd mizukage so we can't say either way.
My point is that he actually seems like the 3rd strongest kage of his time, and that isn't even counting all the past and present kages.
