I'd say most of the time it's an age thing the younger we are the easier impressed/amazed we are. growing older makes us sometimes cynical sometimes overloaded with imagery. The more you've seen the harder it gets to be impressed by stuff, cause you have seen so much. And we keep fond memories of the things we liked as kids and teenagers.
That's also why it feels like the older you are the faster time passes. Life gets monotonous for you so all the days just blend in together and time feels like it's flying. You've seen a lot you've done a lot and stuff just sorta stops being as impressive as it was when you were a child.
Oh yeah, when you're younger there's so many firsts: first day of school, first crush, first kiss, first bf/gf, first dance, etc etc etc... the older you get, the fewer and further these benchmarks get. Still stuff like marriage, kids, career moves, house (lol maybe), but most of the time you grind work and fall deep into a routine.
Gotta keep shaking it up with travel and trying new things so it's not a hot boring blur. I'm hitting mid 30's but I swear I was mid 20's like a minute ago.