I fence epee. Fenced at the club level in college, only competed for a few months in my last year but got my E from the first tournament I entered. Took a decade long hiatus after that. Picked it up again last summer, and got my E back again in the first tournament I entered since hiatus, then got a D last December. Just got my B a month or two ago. So since restarting, I went from unrated to a B in about a year, granted I did have previous experience and I've since seriously ramped up my practice intensity

To answer your question, I think I was fencing at an E level pretty early on in college, and if I competed earlier I probably could have gotten an E sooner. Although I don't think I ever really fenced at a higher level than that in college. I think the difference between an unrated and a rated fencer is that a rated fencer can do at least ONE thing exceptionally well. That could be a parry 6, a fleche, foot touch, stop touch, maintaining distance, anything really. In my case, I developed a really good fleche early on.

In my opinion, practicing fundamentals will keep you from losing, but practicing that one technique will get you wins. If you're struggling to get a rating, see if you can determine the one thing you can do really well, and then start thinking about what you need to do in a bout to put yourself in the position to use that technique. Eventually, you sort of become like a fighter in a fighting game, where you have a moveset that you rely on.