Hi Jacob. Croeso i’r fforwm, welcome to the forum.
Fluency is a very slippery word, and lots of people never feel fluent to themselves, while to the listener they sound perfectly fluent. For too many people fluent is an end of the rainbow prize, never to be achieved.
So, do you mean 100% accurate? No one is, not even a native born Cymro. Those mutations get everyone in the end. But they are understood, so does it matter?
Do you mean you understood everything a native Welsh speaker says? My Welsh neighbours who spoke Welsh to each other for 60 years of their married lives were stymied by the equally native Welsh speaker at the tourist office at the other end of the country and by mutual consent they all turned to English.
Do you mean never having to stop and think about what you’re saying. Practice, practice, practice.
You say you’ve been learning for several years. Are you new to the SSIW community? Have you been using their courses, or principally going to a night class or similar. SSIW, within their materials, encorages you to speak. There’s a reason it’s called SAY SIW.
On top of their online lessons, in more normal times there are regular meetups across the country. Weekly, fortnightly, monthly, in pubs and cafes where people get together to talk. And there are bootcamps where learners have a whole week full of chances to speak only Welsh. In normak times, that is.
There’s also quite an online presence, continuing in these days of gloom. @BronwenLewis quite often talks to people one to one, as do others. Put out a shout. And @nia.llywelyn organises regular groups on line. If you find yourself doing the 6 minute a day course, or the 6 month course, then participating in these groups is part of the deal.
So yes, practice, practice, practice. And for every time someone understands you, remember that feeling, and save it up for a rainy day!