Calculate an Age by Birthday using PHP

<?php 
// PHP 5.3-
function birthday($birthday){ 
    $age = strtotime($birthday);
    
    if($age === false){ 
        return false; 
    } 
    
    list($y1,$m1,$d1) = explode("-",date("Y-m-d",$age)); 
    
    $now = strtotime("now"); 
    
    list($y2,$m2,$d2) = explode("-",date("Y-m-d",$now)); 
    
    $age = $y2 - $y1; 
    
    if((int)($m2.$d2) < (int)($m1.$d1)) 
        $age -= 1; 
        
    return $age; 
} 
 
echo birthday('1981-05-18'); 
 
// PHP 5.3+
function birthday($birthday) {
    $age = date_create($birthday)->diff(date_create('today'))->y;
    
    return $age;
}
 
echo birthday('1981-05-18');

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