I always thought it was just down to this:<p>The year from one's birth to one's first birthday is one's <i>whole</i> life.<p>The year from one's first birthday to one's second birthday is <i>half</i> of one's life.<p>...<p>The year from one's 29th birthday to one's 30th birthday is only 1/30 of one's life.<p>...<p>The year from one's 99th birthday to one's 100th birthday is just 1% of one's life.
I always thought that, as a child, we differentiate, and everything we experience splits into new branches, creating intelligence, whereas when we get older, we assimilate, everything we experience gets merged into a previous experience or understanding, creating wisdom.
I have been thinking this a biological thing...consider another similar example, e.g. seeing a movie, commercial or something for the first time. Regardless of age, subsequent times have always felt faster than the first one to me.<p>From this, I entirely unscientifically surmise that the extra time experience comes from the creation of pathways and whatnot in the brain--which occurs less often the older you get. The more specific explanations could be actual spare cycles in the brain that are only used then encountering something new, or more plausibly, the ratio of conscious vs. unconscious cycles or plain stimulation of the regions responsible for time comprehension.
I think it comes down to novelty.<p>When I'm a regular working stiff, the months seem to fly by because each day is so similar to the last. They all just blend together in your memory, and you find yourself looking back and thinking, "Where did last month go?"<p>Humdrum days are also forgettable and you don't really think about them as you go through the motions. So at the end of the day, there isn't a lot of substance that your mind holds on to. Looking back, it's like they were over in an instant.<p>I remember when I was traveling, some weeks seemed to go on forever, because every day was crammed full of new, interesting experiences. But as soon as I got into a routine, time seemed to speed up again and the days started to run into each other.
When I was a kid, I had the capacity for boredom. I really don't anymore. I suspect that's about it. A child is always looking at the clock, waiting, waiting, itching to get onto the next thing, feeling like the next sensation is too far away.
A bit offtopic maybe, but there's a nice short story from Stephen King about this time perception phenomena.<p><a href="http://en.wikipedia.org/wiki/My_Pretty_Pony" rel="nofollow">http://en.wikipedia.org/wiki/My_Pretty_Pony</a>