I'll say this. Just generalizing. I played and practiced quite hard for about 10 years. I reached A- , give or take. I saw a few others take up the game and reach A+ or AAA in a year. Granted, they are exceptional, but those are the individuals who reach the highest levels, along with those that start playing at 5 or 6 years old. Most have a ton of natural ability.
I quit playing altogether for 25 years. Now at 56 I'm back, and I think I've about reached where I was before the layoff. It's going to be a great struggle to improve further. I can play smarter, and I can virtually eliminate most glaring bad habits, but age is a big factor. All the instruction in the world can't make up for a lazy practitioner, or for someone who's not willing to be objective and change the basics that we've adopted which may be all wrong. We THINK they're fine, and often resent being told that they need to change. We're fond and proud of our basic style, and resist being told to change it.
I agree with the previous poster that a lot of it might be mental. Focus and concentration go back to your childhood, and your perceptions of competition. It's DEEP
. I wish you the best...Tom