I've spent enough time learning Japanese, befriending lots of other people who were learning Japanese, and hanging out on otaku forums to know that at least half of what you hear is... misleading at the very least. Anyone genuinely interested in jumping the gun and learning Japanese should read this: A Friend of Mine Learned Japanese in 1 Year
From what I've witnessed in my own irl observation (and I've met safe to 100 people that have studied Japanese), unless they grew up speaking Chinese or Korean it took them a minimum of 4 - 5 years to get good at the language. I'm talking JLPT N2 - N1 level. And pretty often, it took more than that. Because people learn at different paces.
Now if your only concern is reading, and you genuinely have no interest to ever communicate (speak or write) in Japanese, then you can probably get to an N2 - N1 reading level in 3 years if you study grammar and vocab diligently, and after getting a solid foundation in those read Japanese nonstop. I have known a handful of people like this, but most normal people can't and shouldn't do this. Most people burn out if they go too intensive for too long. Language learning for most people is like the Tortoise and the Hare, slow and steady wins the race. Please don't feel ashamed if you aren't N1 fluent in 3 years, or even 5 years. Because I feel in their push to encourage people to learn Japanese, sometimes Otaku communities unintentionally instill a sense of shame in people who don't learn super fast. Again, if you aren't Chinese or Korean, taking 5 - 10 years to get to JLPT N1 level is entirely normal.
To specify, Koreans have an advantage because their grammatical system is relatively close to Japanese. And many words sound similar as well. If you know Chinese you already know the meanings of most Kanji, which is a huge advantage because this easily knocks out the hardest part of the language for many people. I should also add, anyone that is already multilingual, even if its not in Korean and/or Chinese also has an advantage because their brains are already more flexible when it comes to languages.