DateSinceExtension.php

<?php 

namespace Acme\CoreBundle\Twig;

class DateSinceExtension extends \Twig_Extension
{
    public function getFilters()
    {
        return array(
            'date_since' => new \Twig_Filter_Method($this, 'dateSince'),
        );
    }

    public function dateSince($date)
    {
        $date = ($date instanceof \DateTime) ? $date->getTimestamp() : strtotime($date);
        $since = time() - $date;

        // time, singular, plural
        $periods = array(
            array(60 * 60 * 24 * 365 , 'ano', 'anos'),
            array(60 * 60 * 24 * 30 , 'mês', 'meses'),
            array(60 * 60 * 24 * 7, 'semana', 'semanas'),
            array(60 * 60 * 24 , 'dia', 'dias'),
            array(60 * 60 , 'hora', 'horas'),
            array(60 , 'minuto', 'minutos'),
            array(1 , 'segundo', 'segundos'),
        );

        foreach ($periods as $period) {
            if ($since < $period[0]) {
                continue;
            }

            $numberOfUnits = floor($since / $period[0]);

            return $numberOfUnits .' '. (($numberOfUnits > 1) ? $period[2] : $period[1]);
        }

        return 'agora';
    }

    public function getName()
    {
        return 'date_since_extension';
    }
}

services.yml

services:
    acme.twig.date_since_extension:
        class: Acme\CoreBundle\Twig\DateSinceExtension
        tags:
            - { name: twig.extension }