Time flies as we get older. But why?

Research shows your brain's internal clock runs more slowly as you age--which means the pace of life appears to speed up. Other research suggests that the perceived passage of time is related to the amount of new perceptual information you absorb; when you're young, everything seems new, which means your brain has more to process...which means the perceived passage of time feels longer. There's biochemical research that shows the release of dopamine when we perceive novel stimuli starts to drop past the age of 20, which makes time appear to go by more quickly.

And then there's what bestselling novelist Harlan Coben--the perfect guy to read when you want a long plane trip to fly by--writes in his new book, Don't Let Go.

There are various theories about why the years pass as you get older. The most popular is also the most obvious. As you get older, each year is a smaller percentage of your life. If you are 10 years old, a year is 10 percent. If you are 50 years old, a year is two percent.

But she had a read a theory that spurned that explanation. The theory states that time passes faster when we are in a set routine, when we aren't learning anything new, when we stay stuck in a life pattern. The key to making time slow down is to have new experiences. You may joke that the week you went on vacation flew by far too quickly, but if you stop and think about it, that week actually seemed to last much longer than one involving the drudgery of your day job. You are complaining about it going away so fast because you loved it, not because it felt as though time was passing faster.

If you want to slow down time, this theory holds: If you want to make the days last, do something different.

Makes perfect sense. When we're young, we have plenty of firsts. First day of school. First day of summer vacation. First date. First kiss. First real relationship. First terrible breakup. First real job. First...you get the point. When we're young, life is full of firsts. Time seems to pass more slowly because everything about those moment is fresh and new.

But you can't have a lifetime of firsts--at least not meaningful firsts.

That's when "different" kicks in.

2012 didn't pass quickly; that's the year I had a heart attack (not that I chose to, but still) and then managed to get in sufficient shape to ride a 100-mile Gran Fondo. (Think that year went by quickly? Ha.)

2016 was the year I did 100,000 push-ups. That year seemed to pass really slowly. For part of that year and this, I wrote my book. (Available for pre-order now!) At the time, each day seemed to pass really quickly--since each day meant I was one day closer to missing my deadline--but because I have so many detailed memories, looking back, the year feels like it passed really slowly.

Next year, I will learn to play guitar. I want to test Daniel Coyle's premise that if you practice a skill (really practice, not just put in the time) for an hour every day for a year or two, you won't get 10 or 20 times better--you'll get immeasurably better. (Read Dan's post; it's a great look at why so few people follow a routine of daily, intensive practice...and why, for those who do, it's transformative.)

Don't just float through life. Do different things as often as you can. Learn something new. Try something new. Go somewhere new. Push yourself. Set a goal, even a silly goal, and work to achieve it.

No matter how old you are, your life can still involve the occasional first. And your life can definitely involve any number of "differents."

When it does, the passage of time will slow dramatically. The rate of your experiences and accomplishments will increase dramatically.

Since the most precious thing any of us has is time...shouldn't that be your goal?