As youve gotten older, you may have noticed the years seem to fly by faster and faster. And its not just you: Our perception of time does change considerably as we age .

Alicea Ardito , a northern Virginia therapist who works with older adults, said one of the most common themes she hears in her sessions is that her clients feel their life has gone by too quickly. A phrase commonly used to describe this feeling is that life has passed by in the blink of an eye, she told HuffPost.

Its important to first understand why years feel like theyre speeding by for many of us. One reason is that, as we get older, calendar units like a year become a smaller and smaller proportion of our overall life, said Ruth Ogden, a psychology professor at Liverpool John Moores University in England who studies time.

When you are 8, for example, one year is an eighth of your whole life, whereas when you are 80, its just an 80th, she told HuffPost. This contributes to the sensation of time passing more quickly.

Another reason has to do with how our memories influence our experience of time.

Our brain is not constantly monitoring time, so when we need to make judgments about long periods of time, like days, months or years, we use the number of memories formed in those periods as a guide to how long the periods lasted, Ogden explained.

For example, if you were asked how long it seemed you had been doing X, your brain would look back at how many memories were formed during period X and use that as a guide to duration. The more memories we form during a period of time, and the more vivid and emotional these memories are, the longer we perceive the period to be.