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

I think of it in a purely mathematical way.

When you are 1 year old, the next year will add another 100% to your age.

When you are 100 years old, the next year will add a meagre 1% to your age.

So as you age, each second/day/year are a smaller fraction of your life than any second/day/year you’ve experienced before. Thus periods of time seem less significant as you go through life.