How aging affects your perception of time! It’s a well known phenomenon that years seem to go by faster as you get older. Some say it’s because one year is much shorter relative to your age when you’re 40 than when you’re 10.
Let me offer my take on this.
When you’re 5 or 10 you discover a lot of new things every day, you learn a lot, your brain is absorbing a lot of new information all the time. By the time you’re 40 most likely the pace of your learning has slowed down, a lot of the things you see are not new to you and you don’t have new experiences or make discoveries for yourself so frequently as in younger age. I experience this different perception of time when walking through a new neighborhood. The first time I take that route it seems to go on quite long, I see new buildings, stores, landmarks and see everything through fresh eyes - each new object is analyzed and evaluated thus much more fully experienced, using a lot of my brain’s capacity. As I keep frequenting the same route more often I stop doing this and my brain is usually busy with thinking about something else, not experiencing the moment in the same way as the first time, sort of walking on auto-pilot. I’m sure you’ve had this experience when you get home after a walk from the train station or a bus stop and realize you don’t remember anything from it because you tuned out of your surroundings.
I think the walk example might be a metaphor for your life. You optimize some things in your life such as work or marriage so that you put them on auto-pilot (and with age comes experience and knowledge that allows you to optimize a lot of things in life, exponentially) and you stop fully experiencing them. This puts you in this mode where life seems to move quicker, however it’s not because you’re now 41 and not 40 but because your brain has gotten used to the routine, there are not many new experiences and you tune out to the passage of time, it just slips through much faster.
To combat that you may want to not over-optimize certain areas of your life, experiment with your life, habits and customs, keep learning and doing new stuff and generally challenging yourself in some ways, so that you savor many more individual moments per unit of time.