How does "learning in maturity" change from regular learning? Why do you need a book? Just go find something and learn it...the system couldn't be simpler.
Besides having a kid and spending most of my "free" energy on him (hah -- this is actually learning to parent and the goalpost is still shifting daily) I'm approaching mid-40s and haven't slowed down. My grandma and grandpa died in their 80s and never stopped learning. Don't fool yourself into a deluded stupor, your brain is still plastic.
These are valuable suggestions indeed. As per my spouse, she sees the value of letting me away to fully switch off (hike, surf, other sportish activity) one week or 10 days every 6-8 months. I am much fresher after these breaks.
Maybe I'm fortunate and developed some preternatural ability to learn by taking college classes almost my entire life. But I've never had a problem asking for book recommendations (from professors, the internet, etc) and then reading the book and learning. For example, I've recently worked through a good chunk of Alegbra: Chapter 0. I've read a few rust books cover to cover to understand the language, etc.
Time isn't as available as it used to be when I was a kid. My brain still works the same though. Learning is learning.