Why don't you just set the goal of completely mastering Aikido? Of course mastery would depend on your view of yourself. Wearing any black belt doesn't mean you've achieved a mastery of Aikido. It reflects others views of you, not your view of yourself.
Many times people achieve shodan rank and quit because they feel they have mastered
a martial art. Actually shodan means you've achieved a certain understanding of the basics, you know where the hands and feet are suppose to go. After shodan, you can begin to actually learn Aikido!
If you want to teach, Teach! Volunteer to warm-up the class or substitute for someone else. Start looking at your instructors as teachers. How do they make conscious the unconscious motions of aikido? Do they verbalize, demonstrate? Do they use humor or drama to impress their students? In any given technique are there common mistakes that they recognize? Do your instructors have a class plan? What are the differences between teachers and the way they instruct? How can you use mistakes to encourage students?
Just like you don't need a black belt to achieve mastery in Aikido, you also don't need it to instruct.