As time progresses, we tend to feel that each year is relatively faster.
I propose that the reasoning for this is because of the fact that the proportion of the additional year to one's entire lifetime is decreasing as time progresses.
In other words, if a 5 year old is going on year 6, the additional year is (1/5) 20% of his or her entire life, so therefore the additional year seems to "feel" like a long time. If this individual grows to be 20 years old, the next additional year is (1/20) 5% of their life. I believe this is the reasoning for the feeling of each additional year in one's life to feel "faster."
Any thoughts or other ideas?