I have been playing bass longer than many who post here have been alive. For years, I was mainly self taught, and was mostly a bedroom bassist. I have played in bands, and I have gigged a little. Mostly, I have played with choirs since the 1990’s. About five years ago, I started taking lessons, and I have really been consistent for the last three years. I can see the improvement, but it has become obvious to me that I have some ingrained habits that are very hard to stop at sixty. To be blunt, I do not think I will ever come close to what I might have been if I had started serious study at least thirty years ago. Ideally, I should have stuck to string bass in college. That would have given me a very strong foundation. I do not plan to quit lessons or serious practice. I just know that it is more for personal enrichment at this point in life.
Lots of thoughts on this...
First, Im more or less in the same situation in terms of coming to grips with the level of my skillset. I play in some bands, and a lot of people think I play well, but I know otherwise. I've gotten better at some things since starting double bass studies and jazz studies, but at the end of the day Im mediocre/borderline competent. I was reminded of this fact every time I'd go up to NYC to do combo stuff with the NYJA.
At 52, considering the amount of time I've put into it I should be a lot better than I am. Looking back over my life there are lots of reasons for not being able to play like i would want to. Lack of talent is there for sure, as I really had to work hard to get to the level Im at now.
However, Oftentimes our ability to not do something well isn't entirely our own fault. Environmental issues and geography play a large role in how we develop skillsets..Growing up, I was STRONGLY discouraged to not play, and even practicing unplugged caused problems for me. Than there was the musical crowd i ran with...Most were jammers. People more interested in making noise than playing any form of cohesive, intelligent music. I still run into that to this day. In my immediate area most people are just interested in jamming out as opposed to getting together to work stuff out and play them correctly.
Lastly there were instructors I spent years with that looking back just weren't very good instructors. I wasted a lot of time with some people and it's only within the past year that I found someone who has an approach to teaching an instrument that is logical and makes sense.
Frankly at this stage of the game music is more about personal enrichment for me..The shutdown has taught me that I enjoy just simply sitting down and working off a chart and playing through it, or just sitting down and making noise with my pedals.
As far as the whole " being mediocre " thing goes, my thoughts on that are that the overwhelming vast majority of musicians playing out in any particular local scene are largely mediocre.
I hope when I’m sixty I’m still playing as much as you do, working on improving my craft like you do, and sharing as much helpful, thoughtful content with the bass community as you consistently do. 
