Creating this attribute on the category will cause the system to show age verify prompt for all items in that category.
Go to Items in the main navigation menu, then go to Categories.
Press Custom Attributes in the upper right corner.
Press + New Product Attribute.
Under ATTRIBUTE CODE, enter age_verify.
Under ATTRIBUTE NAME, enter Over 21?.
Under CUSTOM ATTRIBUTE TYPE, select Product attribute / string.
Under FRONTEND INPUT TYPE, select Select.
Press + Add New.
Under VALUE, enter true. Under LABEL, enter True or YES.
Press + Add New again. Under VALUE enter false and under LABEL, enter False or NO.
Under UI COLUMN SIZE IN POS, enter 3.
You can leave the dropdown menu under SHOW ON QUICK UPDATE FORM blank.