>>924 17 years on and off, including 4 years of high school classes (so more time was spent on conversation than in, say, a college elective sequence, but the material didn't get as advanced). Someone who gets past that level and then really applies themselves (especially with modern learning materials) most likely would get to my level in a fraction of the time. My interests were and are too divided for it to have gone any other way; and I took a bit of a break for the past 5 years while I finished off my long overdue degree and then got stuck on an interminable job hunt... but that'd make a long story longer.
I did translations of nerd shit for a while up to that point, but it was frustrating because I was not building appreciable speed nor learning the language beyond the materials I was translating. Aside from the problem of being buried contextlessly in a dictionary, you end up spending lots of time on the task trying to come up with the phrasing you want in the target language if you really want to do it faithfully, which I did (so with that in mind, my words-per-day pace was surprisingly comparable to a professional despite my lower level of understanding).
There are a lot of differing opinions out there about how to acquire Japanese reading skills. None of them aside from "read a shitload of stuff you're interested in, re-read if you didn't understand, and remember it" really sounds right to me (I've heard it said that Frederick Douglass would circle words he didn't know and get back to them later). Naturally, the kanji present a significant obstacle; people make some ado about how the most common ones make up >90% of usage, but downplay that the rarer ones tend to be distinctive words that comprise the important parts of text: someone's name, a scientific or philosophical phenomenon, exactly what and how someone did something to someone else, etc. Like, you're not going to find an interesting story consisting mostly of "Where is the airport?" "This weekend will be cold and rainy" conversational fluff.
I recently started using Anki to shore up some grammatical vocab. Most people use it for studying kanji, but I've got like 1300 down reasonably solid (reading-wise) from just knowing a few thousand words by sight, so I'm putting that off for now. I expect to be capable of passing JLPT N1 someday, but I wouldn't feel that good at it even then.