If I humble myself too much with the 'always a beginner' mindset there's the risk I'll have too little confidence to truly learn and advance. It's all about keeping yourself genuinely modest.
But, of course, from a 'beginner in the grand scheme of things' point of view, Sandan does sound like a reasonable level.
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.