This is exactly what I feel, too, so I deleted my early comment because you summarize it so well. It feels like memory "diff" sizes more than anything else. As

This is exactly what I feel, too, so I deleted my early comment because you summarize it so well. It feels like memory "diff" sizes more than anything else. As you get older fewer things change versus what you've experienced before, so fewer memories take root in that duration of time versus youth. And the memory samples are the tickrate by which we sense the passing of time. I think there may be a minor biological element to this, too. Because of this reduced need to remember new things rapidly, our brain optimizes in other areas and it can be more difficult to retain those things when you need to do so.