I think roughly 1900-1930, before leaded gasoline and also before radio and TV, was the peak. At least for educated elites -- the general population didn't get nearly as much schooling.
But look at physics: Basically all modern theory was developed by 1930. Math too, with the exception of information theory.
But look at physics: Basically all modern theory was developed by 1930. Math too, with the exception of information theory.