It’s almost certainly a mixture of things you’re seeing - some mental health issues occasionally, some is lifelong and normal, some is just when aging you don’t care as much who sees you doing what in your younger days might have seemed embarrassing, in your old age you also have stored a lot more information and context and talking through them helps organize thoughts a little better.

There’s more reasons, but you can see there’s a mixture of reasons why it’s occurring, and each time you see it it’s probably a differently weighted mixture of all these things. My wife has always talked to herself to work things out as she’s planning, also announcing what she’s doing in the next few moments or hours to herself, she also complains about whatever is wrong out loud no matter what it is, but most notably she does this FAR more often when she’s stressed.