But is that a helpful and meaningful definition of "beginner"? Seems to me that OP's original question was asking something analogous to, "When did you start to feel that you were getting your 'sea legs'?" To respond to that saying that you're a nth dan and you still consider yourself the lowliest beginner strikes me as faux humility -- or, who knows, maybe it's genuine humility, but it's not helpful in telling OP what I think he wants to know, which is when (and how) do the pieces start to fall into place.
Ah, so, you understand the question! Care to proffer an answer yourself?
Mostly kidding, but just a little serious...
I myself think "sea legs" are going to vary from person to person. I also have found over the years that everytime I think I'm getting somewhere, I find out I'm not where I thought I was. I had this great german uke the other day at a seminar, I was doing this really relaxed, beautiful heaven and earth throw, and he was FLYING.
Then I took a look at his wrists...they were MASSIVE...so I asked him to REALLY hold me. I couldn't budge. Glad I checked myself...I could have walked away thinking myself a re-incarnation of some Kami...
Sides, I tend to get sea sick anyway...what do I want with sea legs?!?
Ron (his ukemi really was fantastic...too bad I couldn't really throw him)