I guess the point of his post is the YC companies are only attractive to some one below 25 years of age with no family to care about. That would mean the YC companies are all looking for the few talented below 25 yr old people.
The additional advantage of this age group being that they generally have no experience with salary negotiations or normal work-life balance. In fact, if they're coming out of a top CS program, they are probably used to bonkers work-life balance, which is exactly what a startup will demand of them.