I find it difficult to imagine a renaissance man like Thomas Jefferson agreeing that it's okay to stop learning when a person becomes an adult.  It's a disturbing fact that the average American will never read another book after leaving high school, which is probably also why he believes he can figure out most things in life simply by using his "gut".   

Jefferson was a man who never stopped learning.   The architect, inventor, and 3rd President of the United states considered himself a scientist rather than a politician.  Jefferson not only authored the Declaration of Independence, he published the first scientific paper in America on paleontology, as well as a book about the State of Virginia simply so other men could become better farmers like himself.  This polymath never stopped reading and corresponding with friends (as well as adversaries) his entire life.  He even took up brewing after retiring just so he could give his neighbors free beer, living to the ripe old age of 83.