Very good question. I have noticed this, as well. I know the reason, but it's hard to explain it in a way that's clear and understandable. When we are young, time is perceived differently. I remember, for example, how summertime seemed to last forever when I was out of grade school, like from the age of 5-10, and thereafter. One reason, I think, that time seemed to crawl by very slowly, was because I had not lived that long on the earth. At the tender age of ten, a year was an incredibly long time (by my own perceptions). But now, at the age of one and thirty, a year passes by, and it seems to fade away quickly. As we grow older, we have experienced more the passage of more time. So in that respect, what we once thought of as long periods of time seem shorter to us. It also has to do with relativity. For example, whenever I have fun, the time flies by fast...like when I am seeing a good movie, or playing fun video games, etc. But then, if things are boring or unpleasant, the time seems to linger on and on. There are two different kinds of time- Chronos time and Kairos time...but to be honest, I don't remember what the difference is.