I have no idea what they do. I'm a Gen X'er and I qualify for Mensa. But like many other Gen X'ers who qualify for Mensa, I was too cool to be a "joiner." This is in part why there's not many people of my generation.
Also I've know, a few people my age and younger who joined only to find there's only older people at the meeting, and that made them feel weird. So they stopped going.