I have been programming since the 1980s, and professionally since the 1990s. And I am still learning. Recently this has been mainly from studying other people's code.

For example, I work with highly technical code in C with lots of hardware interfaces and mathematical algorithms. The existing code is strictly organized and was written by a very disciplined developer. This level of structure and discipline helps me to write code like that myself.

As another example, I have been browsing through some code Emacs Lisp lately, like the very basic simple.el. As Emacs is "self-documenting", comments are an integral part of elisp to begin with, and developers have clearly taken care to explain their code where they saw fit. Although I think that comments can be evil at worst and are a code-smell at best, good comments can be really valuable, and I can learn from the way Emacs modules have been documented.