function checkDOB() {
  var date = new Date();
  var full18 = new Date(date.getFullYear() - 18, date.getMonth(), date.getDate());
  var dob = new Date(form['yyyy'].value, form['mm'].value, form['dd'].value);

  if (full18 < dob) {
    alert('You must be 18 years or older to be eligible for this offer. Please enter your correct Date of Birth or click Pass to see the next offer.');
    return false;
  }
}

Check Date of Birth

user

JavaScript