code: public static function getAgeByDate(string $sBirthday) : int
      {
          list($iYear, $iMonth, $iDay) = preg_split('/[-.]/', $sBirthday);
  
          $aToday = array();
          $aToday['mois'] = date('n');
          $aToday['jour'] = date('j');
          $aToday['annee'] = date('Y');
  
          $iYears = $aToday['annee'] - $iYear;
  
          if ($aToday['mois'] <= $iMonth) {
  
              if ($iMonth == $aToday['mois']) {
  
                  if ($iDay > $aToday['jour']) { $iYears--; }
              }
              else {
  
                  $iYears--;
              }
          }
  
          return $iYears;
      }
docs: get age by date
  
  @access public
  @param string $sBirthday
  @return int