I am old, have no knowledge at all, and have a lot of jokes.

When you are old, you have no knowledge. There are many jokes, which means you don't know jokes at such a big age. I am old and have no knowledge at all. On the surface, the joke is that you have a handful of firewood when you are old, but in fact you have no knowledge at all. In fact, it means that a scholar is so old and has little knowledge, but he makes a lot of jokes.