pretty much agree with you. You are ready to play the guitar (which I do), when you are ready to pick one up and practice for endless hours. You only master the guitar when you no longer have to think about what you are doing (which I can't).
I think Aikido is pretty much the same.
You only master (insert skill, language, anything) when you no longer have to think about what you are doing. One might say "when it is part of you"...