Alternatively: at some point a person will set into a master set of learning heuristics and the pace of learning will settle into a norm for themselves. Some of these are heuristics others will learn in due time.
Also, the further you push the bounds in any field, the more input it takes to reach bigger understandings. Look at math, many of our kids here could never have heard of math and at age 8 master the concepts of addition, substraction, multiplication, division, fractions, decimals in a couple of weeks. They are really small ideas needing tiny heuristics to understand. Then look at geometry that is pretty content rich.
So, I'm going to say learning can be slow starting, fast in the middle, then slow at the end. Alternatively for some people it is fast, faster, slow...
At some point asymptotic looks pretty plateauish. That is also a caveat for the perfectionist learner, who can't appreciate that it may take 1000 pages of reading to progress the seemingly same functional amount that took half a page when they began studying a new field.
