function to check through a pre formatted birthday (ex: '08/09/1988') and calculates if your over 18.

JailBait Check

// vars
var birthday = '08/09/1988';
var d = new Date();
var month = d.getMonth()+1;
var day = d.getDate();

// double digit month
((''+month).length<2 ? '0' : '') + month
// double digit day
((''+day).length<2 ? '0' : '') + day


// run through the year, month and then day to check if over 18 years old.
var birthdayCheck = function(birthday) {
  var bday = birthday.split('/');
  
  if (bday[2] < 1995) {
    // person is older then 18 already, allow submission
    return true;
  } else if (bday[2] > 1995) {
    // not 18 till at next year, return false
    return false;
  } else if (bday[2] = 1995) {
    // birthday is this year, check the month
    if(bday[0] < ((''+month).length<2 ? '0' : '') + month ) {
      // birthday has already happened this year, allow submission
      return true;
    } else if (bday[0] > ((''+month).length<2 ? '0' : '') + month ) {
      // birthday hasn't happened yet, return false;
      return false;
    } else if (bday[0] = ((''+month).length<2 ? '0' : '') + month ) {
      // birthday is in same month, check the day.
      if (bday[1] < ((''+day).length<2 ? '0' : '') + day ) {
        // birthday has already happened this month, happy late birthday
        return true;
      } else if (bday[1] > ((''+day).length<2 ? '0' : '') + day ) {
        // birthday is coming up, but not quite there yet.
        return false;
      } else if (bday[1] = ((''+day).length<2 ? '0' : '') + day ) {
        // it's your birthday! HAPPY BIRTHDAY, allow submission
        alert('happy birthday');
        return true;
      }
    } else {
      return false;
    }
  } else {
    return false;
  }
  
};


// check to see if birthday validates          
if(birthdayCheck(birthday)) {
	// birthday validated do something
} else {
	alert('Naughty Naugty, you are not 18 as of today');
}