There is one other perception of time as we get older. We realize that we are very rapidly running out of it. Each day becomes more urgent to get the things done that we wanted to do. You never hear the young discussing their bucket lists.

Same thing is seen when going on holidays - The first few days seem to last forever, new experiences, new images . After the first week it then just flies by. Which fits in with both the 'new image' theory and 'logarithmic hypothesis' of time perception.
Doing nothing while waiting for something to happen also seems to alter our the perception of time, which is seen in the common sayings - 'a watched kettle never boils' and 'like watching paint dry' . Which goes against the 'new image' theory of stretching perceived time.
As does those boring school lessons!

I always figured it was because as we age we have more and more experiences for the brain to sort and catalog and compare with every other experience in order to put it them in the right place within the brain.
As our brains are more engaged in these activities, it has less time to mark the passing of time; the time intervals it perceives are spaced farther apart making it seem that time is moving at a much faster pace, even though it it actually passing at the same rate.

I once asked my young sons if time seemed to be going by fast for them. They both answered yes.

Good theories, but does it explain why the new water heater I bought a couple of years ago is actually 10 years old?

The key, I have found at 48, is to banish repetitiveness. Novelty is the only way to slow down time. I spend my life now traveling the world in my van and motorcycle, always trying to find new things to see and do. If there isn't a day where I can look back and say "yep, that was the day I climbed x" or "that was the day I first visited y" then I consider it a slightly wasted day. There are so many more people now realizing that a "normal" life in an office with two kids is so comfortable as to be terminally boring...

The logarithmic scale is built into everything. In the young universe you have big stars forming and blowing up very fast. In the old universe you have only red dwarfs that last trillions of years.

I think our minds, as we get older are preparing us for eternity, whatever meaning you want to apply to the term “eternity”.

My Theory is that there is just More and More Crap that we're Exposed to and Quite Aware of, but that we've already decided that We Don't Need to Bother With Very Much of It.

A friend once jokingly said something worth mentioning here: "When you're ten years old, life goes 10mph, and when you're fifty, 50mph".
The young are busy interpreting and absorbing a lot of information and images, this is certainly true, but that shouldn't stop older folks from doing the same, and even more of it. Some people grow old, and some grow up. Routine is probably the culprit here, as some of the posters allude to.
If you had the luxury (and tenacity) of taking away all the clocks, computers, cell phones, radios and TV's in your home and paid attention only to your circadian rhythms, would that make a difference? Maybe not.