When we were young the summers often seemed to drag by.  Each semester of school seemed to go on and on. The month between Thanksgiving and Christmas seemed to take an eternity.  As we have gotten older the years seem to speed by (can you believe that 2007 was 10 years ago!).

Obviously, time itself does not change.  Why does our perception of time change as we age?  There are a few theories.

1. We gauge time by memorable events, and more memorable events and “firsts” happen when we are younger.
2. The amount of time that has passed relative to one’s age decreases as we age.  When you are 10 a year is 10% of your life.  At age 40 a year is only 2.5% of the years you’ve lived.
3. As we age, we pay less attention to time.
4. Our biological clock slows as we age, making it seem as external time passes quicker.
5. Time stress often leads to the feeling that time has sped up and we often feel more time stress as adults.

Another interesting point – a study found that everybody, regardless of age, thought that time was passing quickly.  And the perception of time did not change with age – we always think that it passed slower when we were younger.

Source and read more here:  Scientific American Blog, and here: Wall Street Journal