Video by Neuroscientist David Eagleman, Director of the Labaratory for Perception and Action at The Baylor College of Medicine
Time seems to move more slowly when you're in a life-threatening situation, but this isn't actually the case. The events of this type of situation are (hopefully) so unique to your brain that it wrote down a good deal of footage for the event. This means that when you replay the moment in your head, there are more details, making it seem like it lasted longer than commonplace memories do.
It makes sense that this would also apply to the feeling that time moves more quickly as we age. When we're younger, so many events within each day can be brand new to us. Our brain is so busy learning and experiencing mentally, physically, socially, and emotionally. As we age, we've kinda been there already. Other than unique life events such as a sparlking new relationship, the birth of a new baby, the start of an exciting new career, or a host of negative life crisis such as death and divorce, life generally becomes routine. Many humans wake to complete the same familair steps, go to work, do their jobs, and come home to exhaust the same chores. We can drive to work and upon arriving, not even remember doing so. There isn't a lot of novelty for the brain to write down in mundane adult life.
This then makes me curious about those whose jobs vary each day, who research and work on larger ideas, or those who choose to get out into the world to explore and try new things more frequently, breaking from the everyday monotony. These more adventerous people, from my experience, tend to more joyful, positive human beings. Could part of the key to happiness be breaking from the everyday normal? Children seem much more joyful than your typical adult. This could easily be for several reasons, but I wonder if you could hold onto some of that child-like mind by creating newness? Could simply entertaining new ideas, continual learning, and exploring new places generate gleeful traction in the human mind?
Book: Why Life Speeds Up As You Get Older: How Memory Shapes Our Past
Book: The Time Paradox