As a fellow late diagnosed ADHD'r (3 years ago at age 45, currently 48) I can relate. Take any and all medical advice with a grain of salt, including mine; if you are on say Adderall or Vynanse the desired effect should actually be increased clarity of thought and increased focus vs "too many thoughts", that said, I'm also an advocate of Sativa strains.
As for learning useful playing techniques/strategies, I suggest getting a real ass kicking old school game like Paragon, Flash Gordon, Seawitch or any other classic solid state machine that absolutely punishes you for taking a wrong shot. I look at a game as being a Wing Chun dummy: every game as being a fight and the goal is to slow the battle down and 90% of an effective defense is just redirecting the energy the game is throwing at you. This means you'll be needing to focus more on blocking strikes (drop catches, dead flips) and keeping in mind how you'll deal with making a recovery as opposed to just focusing on the specific game's objectives.
Now practice, practice, practice. Other "wax on wax off" ideas including turning ball saves and extra balls off, set your machines to two balls instead of three and also setting your tilts tighter and tighter.
