Calculate age based on date of birth (taking into account leap years)

Mainly considering the situation of leap years, if someone is born on 2.29, then if it is not a leap year, then 2.28 will be counted as one year old.                  
                                                                                                                                                                                                                                                                                                        OnFunction Age ($ BIRTH) {
$ Age = Array ();
// $ now = date ('ymd');
$ now = "20110228";
              $nowyear = (int) ($now / 10000);

             $birthday =  $birth % 100;
                                                $ Nowyear-$ BIRTHYEAR;
 If ($ BIRTHMONTH & GT; $ Nowmonth) {
 $ Year-;
} Else If ($ BIRTHMONTH == $ Nowmonth) {
 b ($ Birthday == 29 & & $ BIRTHMONTH = 2) {
/ *                                                                             $year--;                                                                             $nowyear==3200){
                                                                                                                                                                                                                                                                                                                                   (($nowyear%4==0)&&($nowyear%100!=0))){
                                                                                                                                                                                         ;
                                                                 return $year;