function checkBirthday(tYear, tMon, tDay) {
	var mon  = document.getElementById('reqMon').value
	var day  = document.getElementById('reqDay').value
	var year = document.getElementById('reqYear').value
	
	if(mon == '' || day == '' || year == '') {
		if(mon == '') {
			alert('Please select month.');
			return false;
		}
		
		if(day == '') {
			alert('Please select day.');
			return false;
		}
		
		if(year == '') {
			alert('Please select year.');
			return false;
		}
	} else {

		var age = tYear - year;

		if(tMon/1 < mon) {
			age--;    
		} else if( tMon/1 == mon && tDay/1 <= day) {
			age--;    
		}

		if (age < 18) {
			alert("You must be at least 18 years of age.");
			return false;
		} else {
			return true;
		}
	}
}