Thanks for your question. I grant you, it could mean that the strategic thinking of the strategist is still immature. But in context I don't think it does.

Musashi lays great weight on developing keen perception of the moment and its potential. When he says _nama_ 生 'unripe' strategy, I understand him to mean strategy that is settled before conditions have ripened. That's comparable to Knuth's remark about optimizing code. I don't think Musashi means that the strategist is too inexperienced.

Although there is a vein in East Asian military theory about wizard-like long-range anticipation of strategic conditions, Musashi doesn't indulge in that.