There's a couple of other things at play. Back when we were in high school the frame rate of our brains was much faster. Faster frame rates mean more information to process. Overall, times seem to go slower. Your frame rate naturally decreases with age. These effects things like reaction time. Adrenalin in the system also effects frame rates. That's why time seems to stand still when you're in the middle of an existential threat. Frame rate differs from animal to animal. Flies have ridiculously high frame rates, which allow them to dodge the fly swatter. Snails have ridiculously slow frame rates-- about 4 per minute.
The other thing that is going on is familiarity. When I drive an unknown piece of road, I have no idea what's ahead. It may only take a half-hour to get to where I'm going, but it feels like forever. When I'm driving home from work along the same path I travel every day, the time seems to slip by. This is especially true when I'm driving to the farm. It's 63 miles-- about 1.5 hours travel time door-to-door. That 90 minutes flies by know, because every bit of road I've travelled so much, I can anticipate every jog, every mailbox.
Bottom line: In high school, my frame rate was about 20% faster than it is now. If I had to wait 5 minutes for the bell to ring in study hall it was a freaking eternity. Now, the time goes by in a flash. Back in 1976, every season was fresh and new. Now, I know pretty much what every day is going to be like.
One other thing: Back in 1976, if I didn't bring a paperback book or a magazine, I had to sit and wait with nothing to occupy my time. Now I have a smartphone. I can read the news, read email, or even read a Kindle Book.
