My reply is in two parts because there are two different questions linked in this thread.
Firstly,the limit of knowledge would be infinity because there is a vast amount of data on various aspects of our lives, our history, our planets etc. It is so vast that it would take many lifetimes for anyone to even glance it. As I am typing this response, new information is added, new knowledge is being generated. This is again endless. So, in short, knowledge limits are set at infinity. We can just about scrape the outer layer.
Secondly what you have classified as beginner, medium and experts apply to a particular small minuscule area in the world wide pool of knowledge. For instance one may has spent his entire career in studying elephant and would be called as an expert in elephant behaviour and other issues. Similar based on the experience and time spent in that sector one would be labelled as a novice etc.