Hamlet making fun of old men here doesn’t really help him in the like-able department. At least not to me, today. I mean, old men can be funny no doubt. I have found that the one (almost universal) type that every student is happy to dive right in and play is an old man. It’s a release of some kind, a very clear physicality and very different from a young person.
However, there is an old man in my life, approaching a century on the planet. His face is wrinkled (no beard but his hair is white) and his legs are much weaker than they used to be. His wit, too, has faded, along with his hearing. And it’s just not funny at all. It’s painful and all I can do is be amazed how he’s survived this long. The indignities of age are such that it just adds insult to injury to mock the aged.
The self-important? Okay. But not the people already losing everything.
It seems to me that Hamlet satirically attacks Polonius through his suddenly-made-up story that probably does not exist in that book; hence, he says Polonius could become younger if he could move backward -in time.