Why do years feel like they pass by so much faster the older we get?

I feel like upto a certain age, a single year felt massive. Waiting for your next birthday felt like it took forever.

​Then you hit your late teens or twenties, and time just speeds up. You blink, years pass in a flash, and you realize you never actually made the most of it. Quite often you catch yourself feeling like you let years slip by without truly living them.

​Is it because life gets packed with responsibilities and routine, so our brains just blur it all together? Or is there an actual psychological reason time moves so much faster in adulthood?