From Joseph Spenner:

Re: Why we feel “slow motion” during crisis (Dec. 11): Towards the end of the article, you mention why “Time speeds up” as you grow older. I believe there to be a different theory. The passage of time is proportional to how long you have been around.

Simply put: A 10 year old child will perceive 2 years the same as a 40 year old man will perceive 8 years. It’s all relative to how long you’ve been around. Thinking back to when I was a child in the 70s, my brother graduating high school in 1975 seems to have occurred ages before 1977 when we moved to our new house in another part of the city. I would have been 10 years old, and 2 years would have been 1/5 of my life. This was only 2 years! However, today, when I think back to August 1992 when I graduated from college, it doesn’t seem very long ago, even though it was over 15 years!

So, I suspect the passage of time is consistent with the percentage of your life that time spans.