Clearly, perception of the “speed of time” changes throughout ones life. I wonder if this is more due to one's age, or the amount of activity, responsibility, and day-to-day business of one's life?

For example, when someone retires, do they sense that time continues to speed up, because each passing minute is a smaller percentage of their life than the minute before? Or does time slow down because suddenly they have more unstructured time and less daily responsibility?