A social networking system maintains characteristics with its users, with various characteristics, such as age, specified by the users (i.e., “asserted characteristics”). The social networking system selects content for a user based at least in part on the characteristics associated with the user. To account for potential inaccuracies in an asserted age of a user, the social networking system clusters users based on ages of other users connected to users. The online system receives verified ages for users in a cluster from a trusted third party system that maintains more accurate characteristics for users than the social networking system. By comparing the asserted ages for users in the cluster to the verified ages for users in the cluster, the social networking system determines an accuracy of the asserted ages for users in the cluster. The accuracy may be used when selecting content for the users.