It is not that time speeds up as you get older. It is that a year is a smaller and smaller portion of your experiences as you age.
For example when you are five a year represents 20% of everything you’ve ever known or experienced. When you are 50 a year is 2%
Perception of it speeds up. When I was in around 3rd or 5th grade or so, I remember it took at least one hour for the clock to go what appeared to be 15 minutes.
Fact!