Re: Who's eligible to teach Aikido? And what level a sensei should be?
It''s not at all a silly question. The answer may not be very simple though: Every student is different and every black belt test is a little different, so any given group of first dans may very in their skill levels. A gifted teacher requires a different skills set from a gifted practitioner: in ANY field there are people who have the ability to teach practically anything and there highly skilled people who cannot teach if their lives depend on it. Because of this, a good teacher need not be that far ahead of his students and a first dan with good teaching skills would be fine for teaching beginners IF he is sometimes training with his own teachers in order to avoid "drift" into bad habits and mistakes.
If the instructor's lineage is good (his teacher, his teacher's teacher) then you should at least visit the dojo!
My two cents; I'm sure others more qualified than me shall also jump in.