I observe that many people, in becoming adults, experience a slowing of their learning to an almost imperceptible rate. I myself felt the onset of it on the precipice of adulthood. This slowing is natural in the sense that it's both common and socially acceptable. It's also a terrible loss for the individual and their society. Adults who continue to learn are capable of formidible accomplishments. Those who don't will find themselves in an increasingly binding existence.
In this culture in which I grew up, aging reeks of defeat. The uncle who struggles to use email or a web browser finds himself in a precarious position if he's not surrounded by sympathetic helpers. It's difficult to blame the uncle himself, as there exist very many like him. Rather, the blame falls on the society that fails to emphasize the importance of cultivating the mind. This belief that aging is defeat seems to propagate by nature of its defeatism. One needs only to read Viktor Frankl's A Man's Search For Meaning to see that the person for whom hope is absent is the most susceptible.
The responsibility of reforming this aspect of society falls solidly on the individuals that are lucky enough to have the time to change themselves. It's possible to surround oneself with human examples, and in so doing, create a realm of possibility. In aging we become an amalgam of the people who we study and interact with.
Learning is defined here narrowly as the accural of tacit knowledge. Tacit knowledge is a set of working assumptions about how one's environment functions. This could be knowing how a colleage behaves, or how to drive a car. All knowledge of this sort is cultivated in an environment. When the colleage dies and cars drive themselves, the associated knowledge is uprooted. Parts of it may still be useful, but as the environment inevitably changes, the assumptions loosen and degrade. When the assumptions are left untended, the magnitude of their degradation is the integral of the rate of change of the enviroment. Cultivation consists of releasing stale knowledge, tending existing knowledge, and seeking new knowledge.
Gauging whether knowledge will be relevant to a future environment bears strong likeness to gauging an investment. Those who profit are those who can afford to take calculated risks. In learning, this is the intersection of people with time and people with discipline.