A man is not usually ready for the wisdom of philosophy until years of faith and its disappointment, hope and its frustration, desire and its satisfaction, culture and its ripening, and most of the phases which richness of experience brings with it form the mind to receive such a revelation. The middle-aged appreciate it more than the young. This does not necessarily mean, however, that all the young are barred from it. Some may have gone through these phases in former reincarnations so completely as to be well enough prepared. Even so, Nature usually sets the age of thirty or thereabouts as her requirement for initiation into philosophy.
-- Notebooks Category 20: What Is Philosophy? > Chapter 2: Its Contemporary Influence > # 127