In my own experience, as a brain matures, it does not really slow down in its important functions but rather incurs occasional and seemingly inexplicable lapses

In my own experience, as a brain matures, it does not really slow down in its important functions but rather incurs occasional and seemingly inexplicable lapses - the "foggy moments" associated with entering into middle age. Nothing to do about them, since they are an inevitable part of aging. In my business, I do complex and strategic analysis all day long in innumerable situations involving often difficult problems and not once has any lapse of this type affected anything that really counts (I am in my late 50s). At the same time, there is a quickness in grasping large volumes of factual material when one is in his 30s or younger that does recede a bit in the 40s and 50s and beyond. That is why learning a foreign language becomes harder as one gets older - but, in that task, even a 12-year old has advantages over one in his 20s. There are just certain phases of life in which the brain is like a sponge and, if one is bright, all manner of detail can not only be pretty quickly absorbed but made to stick. The lesson here is not to take the quick-absorption phase of life for granted and squander it - that is precisely the time to throw yourself into the deep things of learning (in whatever field) and get the most out of them. Beyond that, though, there is no need to fret. In almost every way, in my experience, an older person is able to function "at a higher level" (to borrow a sport metaphor) in terms of thinking and decision-making than is a younger one. This may stem from other elements that supplement raw brain-power, such as experience, wisdom, and maturity. Thus, in spite of the occasional lapses and the loss of some of the old quickness, I would not trade my current mental capacities for those I had at a younger age even if I could. This piece makes excellent points about the importance of exercise and other forms of mental stimulation being not only helpful but also indispensable to staying sharp. Therefore, as long as you have prepared yourself well when you are young, the rest is a mere continuation of the old pattern, maybe not as vibrant but nothing at all to be dismayed about (at least until dementia sets in!).