Learned chess at 30 (52 now). Never played in a club. I never studied theory, in the opening I must choose my moves based on general principles. I had a stroke in 2014. I have frequent moments where my focus vanishes completely for a few milliseconds. When I regain focus, I lost the grip on the position and I blunder a piece or make a random move. I cant play more than ~10 games at a time.