a. No, you're probably not a bad programmer. Companies who recruit solely based on codility type questions are... How do I put it?... Not smart.

b. Learning things like analysis of algorithms, data structures and other computer science fundamentals is useful, even if you might not use them directly, they will influence the way you think.

It is never too late to start and given an open mindset, willingness to apply oneself and consistent practice, it won't take long to understand the basics of computer science. I usually recommend this is a starting point :

http://interactivepython.org/runestone/static/pythonds/index...