Public speaking humor is only old if your audience has heard it before and if they remember it. Most people don't remember the exact details of jokes, one-liners, and stories. This is not contradictory to the fact that one of the uses of humor is to make your points more memorable.
One of the reasons people don't remember jokes and other pieces of humor is that the humor is usually heard out of context. The humor was not used in conjunction with a point which is the way you should use it in a speaking engagement. The humor was used for entertainment value only and was enjoyed and quickly forgotten.
When you bring back some of this old humor, you will be tying it to your point which makes it acceptable to use in the first place. In the second place, even if some audience members recognize the humor, they probably don't remember the punch line. If you tell it well, even these people will enjoy hearing it again.
The technique to tell a very old joke or story is to tell the audience it is old. This is the one time when you might want to tell the audience you have a joke or story coming. If you don*t tell them that you know it is old, they will likely think you are out of touch. If you tell them you are going to tell an old story or joke, you are telling them you know it's old, but it makes the point so well that you think it is worth telling again.
You will come across jokes and stories that can be updated. Some can be updated as easily as adding a current name. Here is an old politician joke:
Joe the politician said he was so surprised about his nomination that his acceptance speech fell out of his pocket.
All you have to do to update this one is to change the name from Joe to the current politician or association member you want to tease. You could also make this a joke on yourself if you know you are going to be nominated for something. I was so surprised about this nomination that MY acceptance speech fell out of my pocket. Here is another one that can be used for presidents, or to tease any business boss:
A man was alone in a rowboat on the Potomac shouting No! No! No! Someone on the riverbank said, 'Is that guy crazy or what?' Another man fishing said, 'No. That's just one of President Clinton's Yes Men on vacation.' All you have to do on this one is to change the name of the river and substitute your BIG TARGET where you see President Clinton.
When speaking in public a little old humor used properly never hurts.