Earlier quoted context omitted.
Personal anecdote: I'm around the same age as OP and until recently also felt like my thinking was slowing down over the years. I went for many years without an exercise habit. About 5 months ago I started lifting weights. The transformation has defied all my expectations and the biggest unexpected benefit is that my mind has become sharper, faster and more focused. I essentially feel like I've reversed a decade's wo…
Would you mind sharing the routine, or a general outline of how you approached weight lifting from “zero” to “one”? I’m approaching 36 and haven’t lifted anything in 10+ years. But reading sentiments like this is motivating me to start again. I’m just scared honestly - my body has atrophied quite a bit the last 4-5 years at minimum
* I hired a personal trainer. Actually, two of them, scheduled on different days, to reduce the chance that I would saddle myself with a bad one and not know it. After 2 months I let go of the least effective trainer. The trainer(s) were huge at first because having an appointment with someone helped me actually get off my ass and show up, my own willpower alone was always insufficient in the past. They also exposed me to a variety of exercises which is how I learned that I really enjoyed weight lifting (and some other exercises, not so much). Nowadays I just have the one guy once a week doing form checks.
* I joined a very nice gym near my office, again as a motivator. It's easier to attach one habit to another habit, and the habit of going to work is pretty ingrained, so "walk across the street for one more appointment" turned getting into the gym from something hard to something that was basically automatic. My workout is my favorite part of the week now because my gym also has a great jacuzzi and afterwards I get to plop into the jacuzzi, veg out and catch up on podcasts.
* In terms of the "technology" around weight lifting specifically. I'll triple emphasize just hiring a good trainer and just following their instructions at first. But once I started engaging my own brain, I found A) Correct protein/macro intake was bigger than everything else in terms of getting results. Get your daily protein to where it needs to be (which is freakishly high) and same goes for calories (depends on your current body type and intake). B) You don't have to push hard on increasing weight at the beginning at all, nor worry much about how many reps you do, just do what is fun and safe and do it regularly. C) For further education the book Starting Strength and the Fitness Wiki maintained by Reddit's r/fitness are really good. They recommend similar beginner workouts and as an out of shape guy, you can basically start on these immediately as long as you're getting regular form checks and sticking to low weights. (I actually was so weak I had to start with just the bar or even dumbbell variants... once I started pigging out on chicken and whey, that changed very fast, increasing how much I was lifting got easier, and within a couple months I had muscles everywhere.)