Scofield Reference Notes (1917 Edition)Chapter 10
10:1 The proverbs of Solomon. A wise son maketh a glad father: but a foolish son is the heaviness of his mother.
10:27 The fear of the LORD prolongeth days: but the years of the wicked shall be shortened.
A "fool" in Scripture is never a mentally deficient person, but rather one arrogant and self-sufficient; one who orders his life as if there were no God. See, for illustration, Luke 12:16-20. The rich man was not mentally deficient, but he was a "fool" because he supposed that his soul could live on the things in the barn, giving no thought to his eternal wellbeing.
(See Scofield "Psalms 19:9")