It sometimes seems that with each passing year, the days and nights zip by more quickly. If you ever had this feeling, you are not imagining it. Studies of human time perception show that age related changes in the nervous system alter one's sense of time; it really does seem to move more quickly with age. At a meeting of the Society for Neuroscience in New Orleans in November, a psychologist Dr. Peter A. Mangan, reported a study in which he asked people in the different age groups to estimate when three minutes has passed by silently counting one-one thousand, two-one thousand, three-one thousand, and so on. People in their early 20s were accurate within three seconds, and some got it exactly right. People in their 60s estimated three minutes were up after 3 minutes and 40 seconds had passed.