Old Dogs, New Tricks
From time to time I run into a player who got started with guitar "a long time ago", is mostly or completely self-taught and is now wondering how to become more proficient with their instrument and whether the many years of self-instruction will impede future progress.
If you're worried about this, I'd like to start by suggesting that you already are as proficient as you can be, given where you are right now in terms of knowledge and execution. That's a bit new-agey, perhaps... my point is that your self-perceived limitations are not permanent.
Different people have different learning styles. The fact that you're self-taught suggests that you learn by doing. If you didn't then you would have either taken lessons long ago or you wouldn't be playing guitar now. There certainly are things that you can do to improve your mastery of the instrument.
Theory knowledge can only help your playing by helping you to understand how chords are put together, the relationships between chords and scales, and how all of that relates to the fingerboard. Don't stress about having to learn it all at once. A little goes a long way and - so long as you apply what you've learned - is cumulative. Use whatever resources work best for you (books, DVDs, teacher...) and be prepared for gradual progress with occasional "aha" moments.
Technique is a tougher nut to crack. There are two ways to go: find a teacher whose style(s) you'd like to emulate and be prepared to have to work hard to shed any "bad habits" that you've developed during your years of self-schooling, or be introspective about your own style(s) and build upon what you already know.
Your performance and ensemble playing, on the other hand, is relatively easy to improve. Find some like-minded people at about your level of proficiency, get together, and play! Use the music classifieds of your local paper to find people. Even though the ads are probably dominated by twenty-somethings looking to "make it", there are plenty of players in their 40s and 50s just waiting for someone to give them a chance to get together with others simply to play for enjoyment and practice.
I started in the 1960s, but didn't get "serious" about playing until 1999. I took a few lessons to kick-start my interest in theory, and have been studying on my own since then.
Occasionally I'll take time out to figure out what I'd like to develop in terms of technique, style and execution. Even if I come up with a big list of areas for improvement, I'll pick one thing, throw the list away, and focus on improving that one thing until I recognize some progress. Only then will I move along to focus on something else. Solving one problem at a time keeps me from being overwhelmed by what I don't know, which is considerable.
When I ran (and played in) a coffee-house in the 1970s one of the players told me that just about anyone can learn to play the guitar in a day or so, but no guitar player ever truly masters the instrument. Keep that in mind when you think you'll never go any further with the guitar. There's always something to learn.
Likewise, don't get hung up on physical limitations. Focus on what you can do and build your own style around your individual strengths.
My playing has come a long way since 1999. I'm happy with how my playing has improved. But it has been a gradual process and my goals have evolved along with my playing. There's no way I would (or could) have envisioned my current style and technique back in 1999. I turn 53 this year, which goes to show that an old dog can teach himself new tricks.