<?php

        $age = "1985-03-13";
       
        echo age($age);
       
function age($age){   
        list($year,$month,$day) = explode("-",$age);   
        $year_diff  = date("Y") - $year;   
        $month_diff = date("m") - $month;   
        $day_diff   = date("d") - $day;   
        if ($month_diff < 0) $year_diff--;   
        elseif (($month_diff==0) && ($day_diff < 0))$year_diff--;
        elseif (($month_diff==0) && ($day_diff >= 0))$year_diff++;
        return $year_diff; 
}

?>
 

function age($birthday){
        $now = time();
        $dt=$now-$birthday;
        //let us check if current the date is far enought from birthday
        //(>2days), we   can use simlified way to calculate age
        if( !((($dt+172800)%31557600)<345600) ){
                $age=floor( $dt/31557600 );
        }else{
                $datestamp = date("d.m.Y", $now);
                list($current_day, $current_month,$current_year)= explode("." , $datestamp);
                list($birth_year, $birth_month, $birth_day) = explode("-" , date('Y-m-d',$birthday));

                $year_dif = $current_year - $birth_year;

                if(($birth_month > $current_month) || ($birth_month == $current_month && $current_day < $birth_day)){
                        $age = $year_dif - 1;
                }else{
                        $age = $year_dif;
                }
        }
    return $age;
}