We all heard it from our parents growing up and thought it sounded preposterous at the time: "What happened to last year? It flew by
!" they would yell to each other at champagne-soaked New Year's Eve parties. That's because when you're a kid, time seemed to move incredibly slowly. My birthday is only a month from Christmas but I remember when I was 7 that those four weeks felt like eons - now it's all I can do to even bother celebrating my birthday, since it feels like I still have tinsel in my hair.
While we can't put our finger on an exact year when "time speeds up" it happens to most of us - and for real reasons. The first, and largest, is due to what psychologists call the Habituation Hypothesis. For very good reason, our brains want to conserve energy (compared to other animals, human brains use a lot of calories to run). So, once we have gotten used to something - a route to work, doing the dishes or getting dressed in the morning, for example - we start to do it on autopilot, and cease noticing many of the small things that make one day different from another
. This makes time seem to pass much more quickly, since fewer unique moments are being recorded by your brain.
When you are a small child, everything is new, and most days are a learning experience, so your brain is rarely on "auto" and you notice much more, leading to time seeming much slower. The more attention that is paid to each moment, the slower time seems to pass (which makes sense, if you think about it).
There are physical reasons time perception changes too: Dopamine levels drop as we age, which affects our sense of time. And heart rate even has an impact. According to a 2013 research paper
in the journal Attention, Perception, and Psychophysics
, "...variations in prospective timing are caused by two factors: the pulse rate of an internal pacemaker and the amount of attention directed to the passage of time."