We aren’t completely sure. We do know some of the things that influence blood pressure, though, so we can speculate a little as to how these things might cause it to go up as over the course of your life.
The pressure in your system depends on
* How fast your heart beats.
* How hard your heart beats with each beat.
* How flexible your arteries are.
* How much fluid is in your system in general.
* How much your nervous system contributes adrenaline.
All of these things are interrelated. For one thing, as you age, it’s possible that your blood vessels get stiffer, and that may cause your blood pressure to go up. Another possibility is that with more stress in your working years, your adrenal glands release more adrenaline, which also raises blood pressure. Some people are sensitive to salt, and if you eat a lot of salt it can have the same effect. It’s also well known that lasting stress and alcohol use will do it.
Though there isn’t a simple answer to your question, hopefully this gives you a better understanding of how blood pressure works, and what affects it.