However, one interesting thing that Google has now disclosed through their Ad Preferences Manager is that, Google has been guessing a user’s age and gender based on the websites they have visited.
Google says that the gender and age are determined by the websites a user visits. In my case both the Age as well as the Gender were correct. Google does not say as to how they are coming up with that assumption but their algorithm looks pretty accurate for most users and might include data from Google Analytics as well. Of course, this information may not be right always and Google provides users with an option to correct it as well.
Google uses this age and gender information along with other preferences to display personalize ads for the users. If you are not comfortable with Google collecting this information, you can easily Opt out by visiting this page.
You can view your own Age and Gender information by visiting Google Ad Preferences Manager page, however, you will have to be logged in with a Google account to view this information. Do let us know if Google was correctly able to guess it for you or not.