After not being able to find a module that worked quite as we wanted, I created a simple Age Gate module for Drupal 7. This module very basic and has various hardcoded paths in it.
The module redirects all anonymous users to the agegate page and requires that they check the ‘Over 18’ checkbox before they can view content on the site. If they don’t check to box and press submit they get redirected to a page at the path ‘access-denied’ (this is the page we use on our site). The module is coded to allow non agegate access to logged in users, the ‘user/login’ page and the ‘access-denied’ page.
Download it here. Module is provided as is. Agegate Module for Drupal 7