Is it illegal to use a scanner to extract a persons age and gender from their ID at a bar and publish the averages online?

While you may be able to collect the information (from those who are willing to volunteer the information) as part of customer research for an individual business, publishing that data on-line may violate a number of laws. Two exceptions would be as a legitimate part of scholarly research or for law enforcement purposes.

Wow, interesting question. If you were collecting or storing any identifying information, such as if you were storing images of a driver's license or even just a name, that would be a problem under certain federal laws. Don't do that. For just an age and gender, I don't see an immediate problem, but I'd need to do some thorough legal case research before replying further this is the kind of issue that should be thoroughly researched before a good answer can be give. In sum: You should probably consult with someone and have an official legal opinion letter drafted, just to be on the safe side.

I think it is against the California Privacy Act to extract and compile such information, even without publishing on the internet. Even if it were not illegal, it would be terrible for business, because people do not want their privacy invaded by the doorperson at a bar. Doing what you suggest would drive customers away, and rightly so, and would rightly result in invasion of privacy lawsuits. Anyone going to a bar a few times can tell what the general clientele is.