Research shows your brain's internal clock runs more slowly as you age--which means the pace of life appears to speed up. Other research suggests that the perceived passage of time is related to the amount of new perceptual information you absorb; when you're young, everything seems new, which means your brain has more to process...which means the perceived passage of time feels longer. There's biochemical research that shows the release of dopamine when we perceive novel stimuli starts to drop past the age of 20, which makes time appear to go by more quickly.
