<?php
$dia1 = "12";
$mes1 = "02";
$ano1 = "2011";

$dia2 = "20";
$mes2 = "02";
$ano2 = "2013";

$data1 = DateTime::createFromFormat("dmY", $dia1 . $mes1 . $ano1);
$data2 = DateTime::createFromFormat("dmY", $dia2 . $mes2 . $ano2);

$diff = $data2->diff($data1);

echo $diff->format("Diferença de %y anos, %m meses e %d dias.");
echo $diff->format("Diferença total de %a dias");