Well that depends on the world population.
If he had done it it 1914, he would only have killed 2 billion.
If he had done it in 1960, then he would have killed 3 billion.
If he had done it in 1975 ( so now we know why he didn't) he would only have had 4 billion to kill.
So is the question of when armaggedon will come, related to how many he wants to kill?
Interestingly this site ( but dont bother reading it all, its......well you'll see)
puts the world population at 3 billion in Noahs day.
http://ldolphin.org/popul.html
Should he call the Guiness Book of Records?