I know I'm gonna catch flack for this, and it's not a "hard core" opinion.....but I believe to call yourself a musician you have to be performing for people. That could be sitting in a studio recording music to be distributed to others, but really SHOULD be live performing in front of an audience. Playing and singing in your bedroom or den is fine, and you have to develop skills somehow, but the ultimate goal should be "playing out". I've been through the trials and tribulations of putting bands together too many times, and it's almost an impossible task. I'm so frustrated with the process myself, that I'm contemplating something I've NEVER done before.....solo busking. Yes, the possibilities are extremely limited and confining, but at least there's little "band drama". (unless you are schizophrenic)
It's also a fact that the voice, as a muscle, HAS to be exercised regularly, as well as guitar chops, to maintain any level of proficiency.
None of this is meant as a criticism of "hobbyists", and whatever you choose to do doesn't need any approval or endorsement by me. It's just that if you (or anyone) is good at what they do, it should be shared with others.
Not giving you "flak," I promise , but I wholeheartedly disagree, at least in terms of if you're not playing live you're not really a musician. So the Beatles after 1966 weren't full-fledged musicians anymore? (The most obvious example I could come up with.)
I played in bands from my teen years through mid-twenties, until hearing damage and pain (hyperacusis) forced me to quit. That was in the mid-nineties. About four years ago I picked up the guitar again and began writing more songs. Last year my old band got together long-distance and recorded four new songs to put up on Bandcamp. My ears are a lot better than they were at their worst, but live performance is still pretty much physically out of the question for me. From here on out it's playing solo at home, writing songs, and recording them with my bandmates long distance (four guys, four different states!). That said, having music back in my life after decades without playing has lifted my spirit more than I could ever imagine.
I'm comfortable saying I'm a musician. That's a term that fits a lot of different situations.
End of Flak Attack!
For the OP -- when I picked up guitar again after those decades off, I was like "Wow, I really suck now!" A few weeks later I was back in the saddle. Don't worry, it really is like riding a bicycle.