Physiologically, man does not reach puberty until he has already completed a fifth of his normal span of life. Let us compare this with the ratio in the case of a mouse, which lives three years and starts breeding at the end of three months. This is a ratio of twelve to one. The mouse’s ratio is much more nearly typical of the large majority of mammals than is the human ratio.
Puberty for most mammals either represents the end of their epoch of tutelage, or is well beyond it. In our community, man is recognized as immature until the age of twenty-one, and the modern period of education for the higher walks of life continues until about thirty, actually beyond the time of greatest physical strength. Man thus spends what may amount to forty per cent of his normal life as a learner, again for reasons that have to do with his physical structure. It is as completely natural for a human society to be based on learning as for an ant society to be based on an inherited pattern.
– Norbert Wiener, The Human Use of Human Beings (1950)