ELI5: Why does time seem to speed up as we age?

Imagine your life is a really long movie.

When you're little, everything is new! Going to the park for the first time, learning to ride a bike, seeing fireworks – these are all big, exciting events. Your brain is busy making lots of new connections for each of these things. Each "first time" takes up a lot of space in your memory movie.

As you get older, you do more things you've already done. Going to school is normal, eating breakfast is routine, and even birthday parties become familiar. You're not making as many new connections because you already know what to expect. These familiar things don't take up as much space in your memory movie.

Think about it like this:

• Young: Lots of "firsts" = long, detailed scenes in your movie. Many neural pathways are being formed.
• Old: Lots of "repeats" = short, quick scenes in your movie. Fewer neural pathways are being formed.

Older people, with more familiar experiences, have fewer "new" scenes. Their movie feels shorter, so time seems to speed up. The proportion of new experiences versus total time shrinks as one ages.

It's all about how much new information your brain is processing and remembering. More new stuff = slower time. Less new stuff = faster time. This is related to how our perception of time is affected by memory and novelty.