I’ve been playing for a little over three years now (3 yrs from Jan 2013).
We all learn at different rates. And it also depends on previous musical experience. For instance, I played guitar (and piano) for many years before I started to learn the banjo so that most of my learning is focused on the right hand.
And it also depends on your practice routine. Again me, I have a lot of free time so I practice at least a few hours a day.
For me, learning the banjo has been all about repetition. So you play a song with a G lick. Then you play another song with the same G lick and another and another. So you repeat this G lick maybe 25 or 50 times a day by playing these songs over and over again. And eventually you’ve played that lick so ofter that your hands automatically remember it. So playing a G lick becomes easy at that point.
Now for me, there was a minimum number of licks and phrases and hand positions I needed to learn like that to get to a tipping point. Now, most songs are pretty easy for me to at least get to sound halfway like they should.
So I think you just need to keep plugging away there. Be confident that every day you practice you will show a little improvement and that one day you’ll get to that tipping point.
I will say though that I learned Nashville Skyline about 10 months in. It took me quite a while to getting it sound halfway decent (and it probably still sounds only halfway decent when I play it now!). Maybe a year (I don’t really remember) from when I started (I still play that song every day). It doesn’t really have a melody so it’s more about riffing which may make it harder to make sound like it should.