This is a simple cloneable showing how to use some Javascript and a modal overlay to gate content based on the birthday and calculated age of a user visiting the page or site.
The code in the page settings takes a form submission of month, day and year of the person's birthday, calculates their age against today's date, and then validates if they are 18 years or older. If they are over 18, then a cookie will be added to their browser and the overlay will be hidden from then on while browsing the site unless they clear their cookies. If they are not over 18, then the form submission showing the success state as an error message noting they aren't allow to view the content.