In Ten Tips on Improving Your Programming Skills, "Practicing" is emphasized. Going through source code in an open source library can be very helpful. Writing comments for that code, and most importantly, making changes to that code can help you gain more understanding of powerful techniques.
I really support the idea of going through libraries. After 6 months of using Struts 1.3, I sat down and went through the Struts source code and even downloaded a copy of Tomcat's source code. Examining this framework and Java Servlet container helped me understand what was going on under the hood. It helped me make better use of the frameworks I needed to use, and it helped me find and fix those pesky bugs that occurred in the software.
In this Stack Overflow post, http://stackoverflow.com/questions/3605337/reading-source-code-to-improve-programming-skills-python, some of the respondents suggest learning a new language every year. I'm a fan of this one. When I learned a little bit of Python and Django, I felt like some of the concepts of the request/response cycle from Java Servlets was similar to what was happening in Python. Realizing that many of the frameworks we use in different languages are just abstractions that share similar concepts reinforced what I already knew about the Web and helped make it easier to visualize once again what happens under the hood.
In this article, they suggest analyzing what you've done in the past. Code I wrote a year ago just isn't as good as code I write today. I've gone back and reviewed code I've written previously and have been able to improve it thanks to both new experiences as well as seeing the code from a different perspective after not thinking about it for awhile.
In summary, the only limits on us are those we place upon ourselves. You can do anything that you put your mind to. If you've hit a plateau, it's most likely because you are burned out. If you're not burned out, then perhaps your learning techniques are flawed, and the information in the above resources may help you discover techniques that pull you out of your funk.