Age restrictions

I'm trying to figure out a way that people can enter there age, and if they enter a number under 18 it restrictions them, or tells them they must be 18 or older. 

You could do this using some conditional logic on your form and set it to if the field doesn't match the correct age or backlogged date then the submit button wouldn't show up or even show other parts of the form to allow them to complete it if they were the correct age.

Example: - 

If " Are you 18 or Older = YES " and " Birth Date is BEFORE 3/5/1996 " then you can continue the form. But if those conditions are not met then the form will not allow it.

http://form.jotform.us/form/40616298292157