Eli5: Why, if at all, does it seem like the years go quicker as you get older?

Question

I hear a lot of people making that remark, that the years go by quicker as you get older.
For me, at least, it seems like that’s only the case if nothing much changes in my life in that year.
To me, years seem to feel like they go slower if there’s lots of new/different things happening.

In: 348

Answer 1

A year as a percentage of how long you’ve been alive gets smaller the longer you live. At 1 years old, it’ll take 100% of your then lifetime to get to 2 years old. At 99 years old, it’ll take approximately 1% of your then lifetime to get to 100 years old. Therefore, your perception of how long a year is relative to your overall then lifetime gets shorter the older you get.