I'm my own experience, I've found that it is hard to learn about something if you're goal is to just learn about it. I tried picking up C++ when I was about twelve (eight years ago), but could never really get into it. The problem was that I wanted to learn how to code, but I didn't have anything that I really wanted to code. I didn't have any projects that I wanted to do that required me to learn C.
Later, in college, I was asked to create a state machine and combinational logic model of a simple processor for one of my computer design classes. I ended up writing the entire thing in java (well over 3000 lines). Even though learning java was probably just as hard as learning C, I was able to do it in just a couple months because I had a project that I was interested in to motivate me.
If you want to develop a high level understanding of computers, make a project out of building one from parts you buy online. If you want a more in depth understanding, try creating a model of a simple computer in a high level programming language (if you do this, VHDL or Verilog would be MUCH better than java...).
You will learn everything you ever wanted to know from the research you will have to do to finish the project, and working towards a goal will keep you motivated.