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…
My girlfriend got sick and now I have a part time caring responsibility that’s mostly about doing chores and errands. I’m in better physical shape now and oddly feel more capable at my engineering job.
But when I had kids it forced me to move and do things. Now I feel better in my '40s than I did in my '30s.