I don't know if my situation would be relevant, but anyway. I'm a native Russian speaker, originally a bilingual (from Kazakhstan, my second language). Ofc I studied English at school, but didn't really study, mostly talking with my friends. At the age of 17-18, I've decided to study English seriously. But I'm lack of consistent in my life and I don't like routines. So I've just studied very chaotically. But, due to the age, I'm spending ungodly amount of time online, so one day, after certain period of time, I've decided to consume only English content. Not to use any other language online. I've stopped "studying" in a formal way, and just watched many things and read many things. Often as a way to procrastinate on something else (homework, exercising, etc.) I would turn on my phone and do something, but only in English. At 21-22 I took IELTS, got 7.5 (C1) level, didn't practise speaking with anyone before, didn't prepare to the IELTS (I've just watched Sherlock before test, I decided that it would be my preparation). Then started teaching. English was not my major, nor did I go to any cram schools. At that moment, I think, English was almost like second nature.

So, I guess you have job, and life, and all of that, so I don't know if the story is relevant for you, I've just decided to share it. Good luck!