This is a small snippet to check if a string is a correct date.

date_validator.php

$compare = "31-10-1991";

// first validate the format...it could be: 24-05-2013,24/05/2013,24.05.2013,24-5-2013,24.5.2013,24/5/2013...or something like that(at this point we've just validated the format...not the date)

if(preg_match('/^(3[0-1]|[0-2]?[0-9])[\/.-](1[0-2]|0?[0-9])[\/.-][0-9]{4}$/',$compare)){
  $date_parsed = preg_split('/[\/.-]/', $compare);
  
	//if the format is correct we're going to see if the date is valid....for example: 31-02-2013 should be invalid....
  
  if(!checkdate($date_parsed[1],$date_parsed[0],$date_parsed[2])){
    	echo "invalid";
    	//  ...whatever you want to do if is invalid ....
    }else{
    	echo "valid";
    	//  ...whatever you want to do if is valid ....
    }
}else{
	echo "invalid";
	//  ...whatever you want to do if is invalid ....
}