Assuming you mean programming professionally (i.e. most of every day), then five years is around the point where you become self-aware and realize your code isn't as awesome as you thought. Also, remember that if you see code published on the Internet, it was probably extremely polished, and likely written by someone who has had quite a lot of experience in a particular area.
By having to maintain my code, I learned to write simple, concise, well-documented code. Nothing teaches you about bad programming practices better than having to maintain your own code after six months or a year away from it. I've also learned that iteration is key to quality. The first time I create something, it's basically crap. By about the third time I've tackled the same sort of problem, I have some pretty good insights, and come up with vastly improved solutions. Of course, people see the output of the 3rd iteration and think I'm a brilliant, insightful programmer, not realizing that -- like everyone -- it didn't happen on my first try.
By having to maintain my code, I learned to write simple, concise, well-documented code. Nothing teaches you about bad programming practices better than having to maintain your own code after six months or a year away from it. I've also learned that iteration is key to quality. The first time I create something, it's basically crap. By about the third time I've tackled the same sort of problem, I have some pretty good insights, and come up with vastly improved solutions. Of course, people see the output of the 3rd iteration and think I'm a brilliant, insightful programmer, not realizing that -- like everyone -- it didn't happen on my first try.