Asking people what their regrets are is the question that I think is
depressing, meself. That question was more implied than asked directly - but I
understand you were asking if this mood if ruefulness is common to getting older, or is it just you. I don't see it as a common experience to getting older from my observations.

In fact, it can often be the reverse; as you get older, you value the positives in life more than before. You should dwell less on what went wrong than what goes right.

They said, perhaps what you are experiencing is the realization that you don't ' know it all' the way you ( thought you ) did when you were younger. You are able to see the shades of gray of a world you once reduced to black and white, a world of easy answers.This awareness usually starts in your 40s btw, But if what you're doing is replacing the arrogance ( and naïveté ) of youthful surety with an ability to see and question the complexities of human interaction - then that is a sign of maturity and wisdom imho.

There's a line from a pop song that goes 'the more I know, the less I understand' Perhaps that's what you are talking about.