Why does time speed up for older people?

I've come across two recent articles recently on how our experience of time is our own invention - "mind time" - that can be faster or slower than clock or calendar time. I find myself incredulous at how fast time seems to pass now compared with my recollection of when I was a 30 or 40-something and felt large periods of leisure in the midst of what was a much more complex (and productive) life than my current retired life (at 71 years of age). In general older people are more likely than younger to report that the last decade has passed quickly. The Friedman piece has a great quote from William James, who argued that the apparent speed of time's passage was a result of adult's experiencing fewer memorable events:

“Each passing year converts some of this experience into automatic routine which we hardly note at all, the days and the weeks smooth themselves out in recollection to contentless units, and the years grow hollow and collapse.”

From Friedman:

Why, then, do older people look back at long stretches of their lives and feel it’s a race to the finish? Here’s a possible answer: think about what it’s like when you learn something for the first time — for example how, when you are young, you learn to ride a bike or navigate your way home from school. It takes time to learn new tasks and to encode them in your memory. And when you are learning about the world for the first time, you are forming a fairly steady stream of new memories of events, places and people.

When, as an adult, you look back at your childhood experiences, they appear to unfold in slow motion probably because the sheer number of them gives you the impression that they must have taken forever to acquire… Most adults do not explore and learn about the world the way they did when they were young; adult life lacks the constant discovery and endless novelty of childhood.

Studies have shown that the greater the cognitive demands of a task, the longer its duration is perceived to be…Is it possible that learning new things might slow down our internal sense of time?…It’s simple: if you want time to slow down, become a student again. Learn something that requires sustained effort; do something novel…Take a new route to work; vacation at an unknown spot. And take your sweet time about it.

The second piece, by Maria Popova article points to Hammond's recent book "Time Warped: Unlocking the Mysteries of Time Perception" and offers a synopsis through multiple quotes, including descriptions of how fear slows down subjective time.

…when people with arachnophobia were asked to look at spiders — the very object of their intense fear — for 45 seconds and they overestimated the elapsed time. The same pattern was observed in novice skydivers, who estimated the duration of their peers’ falls as short, whereas their own, from the same altitude, were deemed longer.

...and the Holiday Paradox

…the contradictory feeling that a good holiday whizzes by, yet feels long when you look back.” (An “American translation” might term it the Vacation Paradox.) Her explanation of its underlying mechanisms is reminiscent of legendary psychologist Daniel Kahneman’s theory of the clash between the “experiencing self” and the “remembering self”….We constantly use both prospective and retrospective estimation to gauge time’s passing. Usually they are in equilibrium, but notable experiences disturb that equilibrium, sometimes dramatically. This is also the reason we never get used to it, and never will. We will continue to perceive time in two ways and continue to be struck by its strangeness every time we go on holiday.

...the difference in the number of novel experiences at different ages:

…we are most likely to vividly remember experiences we had between the ages of 15 and 25. What the social sciences might simply call “nostalgia” psychologists have termed the “reminiscence bump”…The key to the reminiscence bump is novelty. The reason we remember our youth so well is that it is a period where we have more new experiences than in our thirties or forties. It’s a time for firsts — first sexual relationships, first jobs, first travel without parents, first experience of living away from home, the first time we get much real choice over the way we spend our days. Novelty has such a strong impact on memory that even within the bump we remember more from the start of each new experience.