Yes, there is an age restriction for using FuckBookOfSex. Users must be 18 years of age or older to use the app. This is a safety measure to ensure that all users are of legal age and that no minors are exposed to inappropriate content. The app takes measures to enforce this policy by requiring users to provide proof of their age when signing up for an account. All in all, this feature provides a secure environment for users who wish to find casual encounters and engage in adult activities.