Why does time feel like it moved slower when I was younger?

A common reason is that time is judged partly by how much newness and attention your brain has to process, and partly by how you remember periods later.

A few well-supported ideas:

• Proportional effect: a year is a much larger fraction of your life when you’re 5 than when you’re 50, so long stretches can feel longer in childhood.
• Novelty and memory: childhood usually contains more first-time experiences, so those periods create denser, more distinctive memories. When you look back, they can feel longer.
• Routine in adulthood: as life becomes more repetitive, fewer memorable milestones get stored, so weeks and months can seem to blur together in hindsight.
• Attention and emotion: when you’re engaged, excited, stressed, or constantly changing tasks, your sense of time can speed up or slow down.

There are also biological factors involved, but they’re more complex than a single simple explanation. Aging, attention, sleep, stress, and mental health can all affect time perception.

So the short answer is: childhood often feels slower because it contains more novelty, more vivid memory formation, and a smaller life perspective.