In just a few lines, the speaker looks back at his younger self with a mix of mockery and tenderness. He calls himself "a long bag of folly," a gangly, foolish figure who "looks better than he thinks." That line suggests a young man who was awkward and unsure inside, even if he seemed fine from the outside. Then comes a grander, funnier image: "a little king of drink." The word "little" undercuts the crown. He ruled over nothing but his own bottle, and he knows it.
The last stanza shifts the tone. "For the fool may be / a cunning scribe" hints that the foolishness wasn't wasted. The young man who stumbled around may also have been watching, collecting, and learning to write. The mood is self-deprecating but quietly proud, like someone laughing at an old photograph while admitting that the person in it was already becoming who he is now.