Why not? I like writing code, understanding code, and solving problems by using my skills to code.

I have a plan that includes retirement savings. At my current rate, I could comfortably retire by the time that I'm 40, but I like working with complex systems, in particular complex computer systems. I tend to write code to understand and modify those systems. Why can't my plan include continuing to convince people to pay me to do what I like and have acquired skill in?