When I was One-and-Twenty Foolishness and Folly Quotes

Here, the speaker is playing off the basic idea that young = stupid.

Calling someone else wise means that, well, our speaker is comparatively less-than wise. That's another name for foolishness, friends.

Here's the moral of the story: young man grows older. In so doing, he gets over his youthful folly. He's growing up, see? We can tell that he gets the point – if only because he starts to repeat himself to emphasize his point!