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.

I'm well past 40s and haven't seen? (There are some days when I don't learn anything, but that only happens if I'm really, really careful.)

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.