$(document).ready(function(){
    var now = new Date();
    var datetime_regex = /^(\d{4})-(\d{1,2})-(\d{1,2}) (\d{1,2}):(\d{1,2}):(\d{1,2})$/;
    $('.review_age').each(function(){
        var matches = $(this).text().match(datetime_regex);
        if(!matches){return;}
        var time = new Date(matches[1], matches[2]-1, matches[3], matches[4], matches[5], matches[6]);
        var span = Math.round((now - time) / 1000); //span は秒数
        var value, unit;
        if(span < 60){
            value = span;
            unit = '秒';
        }else if(span >= 60 && span < 3600){
            value = span / 60;
            unit = '分';
        }else if(span >= 3600 && span < 86400){
            value = span / 3600;
            unit = '時間';
        }else if(span >= 86400 && span < 2592000){
            value = span / 86400;
            unit = '日';
        }else{
            value = span / 2592000;
            unit = 'ヶ月';
        }
        $(this).text(Math.round(value) + unit + '前');
    });
});