Re: When did you stop being a beginner in Aikido?
The problem is that beginner and advanced are more relative than absolute terms. So they only really make sense in some kind of context, i.e., compared to who(m). That goes for any field unless there's a theoretical logical ceiling for the skill set,(i.e. a point at which you are literally 'perfect' and it's simply not possible to be better) -- this is true of math or music or most things you can study, as much as of Aikido.
The question of what word you use to define yourself isn't unique to Aikido, either; it happens with anything you study enough to have some sense of how far a person could in theory go. Random example: in my last year of high school I really felt like I was doing 'advanced' math when I took calculus, but pretty soon in university and a couple math courses into my engineering degree I felt more like a beginner, and not because I was doing it that badly, just because I started to see how immense and deep the field truely was and how vastly more advanced it was possible to go than my (now seemingly incredibly piddling) little first and second year calculus, algebra, differential equations, etc courses. People spend decades studying, as a full-time job, just a small subset of just one of those. But on the other hand the math I learned is still advanced compared to high school math or elementary school arithmetic.