Bypass YouTube Age Verification: Redirects from the age verification webpage to the comments webpage and then embeds the age-restricted video. Based on @display's "Bypass youtube age restrict" (http://userscripts.org/scripts/show/88856/).

Bypass YouTube Age Verification 1.01.js

// ==UserScript==
// @name Bypass YouTube Age Verification
// @version 1.01
// @description Redirects from the age verification webpage to the comments webpage and then embeds the age-restricted video. Based on @display's "Bypass youtube age restrict" (http://userscripts.org/scripts/show/88856/).
// @author XP1 (https://github.com/XP1/)
// @namespace https://gist.github.com/1147490/
// @include http*://youtube.*/verify_age?*
// @include http*://*.youtube.*/verify_age?*
// @include http*://youtube.*/all_comments?*&embed=1*
// @include http*://*.youtube.*/all_comments?*&embed=1*
// ==/UserScript==

// Battlefield 3 Physical Warfare Pack Gameplay Trailer:
// http://www.youtube.com/watch?v=G-ukxgldpOo

/*jslint browser: true, vars: true, white: true, maxerr: 50, indent: 4 */
(function (console, topWindow, windowLocation)
{
    "use strict";

    if (window.self !== topWindow)
    {
        return;
    }

    var userScript =
    {
        name: "Bypass YouTube Age Verification"
    };

    function removeEventListenerAfterFiring(numberOfTimes, callback)
    {
        var remaining = numberOfTimes;
        return function listener(event)
        {
            remaining -= 1;

            if (remaining <= 0)
            {
                var target = event.target;
                var type = event.type;
                target.removeEventListener(type, listener, false);
                target.removeEventListener(type, listener, true);
            }

            callback();
        };
    }

    var handleException = function (theFunction)
    {
        try
        {
            theFunction();
        }
        catch (exception)
        {
            console.log("[" + userScript.name + "]: Exception: " + exception);
        }
    };

    var playerSizes =
    {
        EMBED_SMALL: {width: 425, height: 349},
        EMBED: {width: 480, height: 390},
        STANDARD: {width: 640, height: 363},
        EMBED_MEDIUM: {width: 640, height: 510},
        EMBED_LARGE: {width: 960, height: 750}
    };

    var options =
    {
        playerSize: playerSizes.STANDARD,
        playerArguments:
        {
            // Documentation: http://code.google.com/apis/youtube/player_parameters.html
            // String or boolean ("0" or "1") only. Null is the default that will embed without parameter and argument.
            autohide: {parameter: "autohide", value: "2"},
            autoplay: {parameter: "autoplay", value: true},
            border: {parameter: "border", value: null},
            closedCaptions: {parameter: "cc_load_policy", value: true},
            progressBarColor: {parameter: "color", value: null},
            primaryBorderColor: {parameter: "color1", value: null},
            controlBarColor: {parameter: "color2", value: null},
            controls: {parameter: "controls", value: null},
            disableKeyboardControls: {parameter: "disablekb", value: null},
            enhancedGenieMenu: {parameter: "egm", value: null},
            enableJsApi: {parameter: "enablejsapi", value: null},
            fullscreen: {parameter: "fs", value: true},
            highDefinition: {parameter: "hd", value: null},
            annotations: {parameter: "iv_load_policy", value: "1"},
            loop: {parameter: "loop", value: false},
            modestBranding: {parameter: "modestbranding", value: null},
            origin: {parameter: "origin", value: null},
            playerApiId: {parameter: "playerapiid", value: null},
            playlist: {parameter: "playlist", value: null},
            relatedVideos: {parameter: "rel", value: null},
            showInfo: {parameter: "showinfo", value: false},
            showSearch: {parameter: "showsearch", value: null},
            startTime: {parameter: "start", value: null},
            theme: {parameter: "theme", value: null}
        }
    };

    /**
     * Store the video data.
     * Use the "find" functions to find the data first before calling the "get" functions to return the private variable.
     * If a "find" function fails to find anything, then the default value stored in the private variable will be returned.
     */
    var video = (function ()
    {
        var uri = windowLocation.href;
        var uriProtocol = windowLocation.protocol;
        var uriHost = windowLocation.host;
        var uriPathname = windowLocation.pathname;
        var uriStart = (uriProtocol + "//" + uriHost);
        var uriEnd = (windowLocation.search + windowLocation.hash);
        var id = null;

        var publicMembers =
        {
            getUri: function ()
            {
                return uri;
            },
            getUriProtocol: function ()
            {
                return uriProtocol;
            },
            getUriHost: function ()
            {
                return uriHost;
            },
            getUriPathname: function ()
            {
                return uriPathname;
            },
            getUriStart: function ()
            {
                return uriStart;
            },
            getUriEnd: function ()
            {
                return uriEnd;
            },
            findId: function (theUri)
            {
                if (typeof theUri === "undefined")
                {
                    theUri = uriEnd;
                }

                if (typeof theUri === "string")
                {
                    theUri = window.encodeURIComponent(theUri);
                    handleException(function ()
                    {
                        var idRegex = /(v=|v%3D|v%253D|\/|%2F|%252F)([\w\-]{11,})/g;
                        id = idRegex.exec(theUri)[2];
                    });
                }
            },
            getId: function ()
            {
                return id;
            }
        };

        return publicMembers;
    }());

    function bypassAgeVerification()
    {
        video.findId();

        if (video.getUriPathname().indexOf("/verify_age") !== -1) // Redirect to comments webpage.
        {
            if (typeof video.getId() === "string")
            {
                windowLocation.replace(video.getUriStart() + "/all_comments?v=" + video.getId() + "&embed=1");
            }
        }
        else if (video.getUriEnd().indexOf("embed=1") !== -1) // Embed video on comments webpage.
        {
            handleException(function ()
            {
                var topWindowDocument = topWindow.document;

                function removeElements()
                {
                    function removeElement(element)
                    {
                        if (element !== null)
                        {
                            element.parentNode.removeChild(element);
                        }
                    }

                    var videoThumbnailsElement = topWindowDocument.getElementById("video-reference-info");
                    var videoRuntimeElement = topWindowDocument.querySelector(".runtime");
                    var videoThreadedCommentsOptionsElement = topWindowDocument.getElementById("threaded-option");

                    removeElement(videoThumbnailsElement);
                    removeElement(videoRuntimeElement);
                    removeElement(videoThreadedCommentsOptionsElement);
                }

                function injectHtml()
                {
                    function generateArguments()
                    {
                        function toString(value)
                        {
                            if (typeof value === "string")
                            {
                                return value;
                            }
                            else if (typeof value === "boolean")
                            {
                                return (value ? "1" : "0");
                            }
                            else // Unknown data type.
                            {
                                return "";
                            }
                        }

                        var result = "";

                        var playerArguments = options.playerArguments;
                        var i = null;
                        for (i in playerArguments)
                        {
                            if (playerArguments.hasOwnProperty(i))
                            {
                                var playerArgument = playerArguments[i];

                                var value = toString(playerArgument.value);
                                if (value !== "")
                                {
                                    result += ("&" + playerArgument.parameter + "=" + value);
                                }
                            }
                        }

                        return result;
                    }

                    var playerSize = options.playerSize;

                    var embedHtml = "<iframe width=\"" + playerSize.width + " \" height=\"" + playerSize.height + "\" src=\"" + video.getUriStart() + "/embed/" + video.getId() + "?"
                        + (generateArguments())
                        + "\" frameborder=\"0\" allowfullscreen></iframe>";

                    var videoDetailsElement = topWindowDocument.querySelector(".vfacets");
                    var videoDetails = videoDetailsElement.innerHTML.split(/<br\/?>/g);
                    videoDetailsElement.innerHTML = "<h1><h3>" + videoDetails[2] + "</h3></h1><br/>" + videoDetails[1] + "<br/>" + videoDetails[0];

                    var videoTitleElement = topWindowDocument.querySelector(".vtitle");
                    videoTitleElement.innerHTML = videoTitleElement.innerHTML + "<br/><strong>" + videoDetails[1] + "</strong><br/><br/>" + embedHtml;
                }

                function replaceTitle()
                {
                    var titleElement = topWindowDocument.querySelector(".vtitle a");
                    if (titleElement !== null)
                    {
                        topWindowDocument.title = titleElement.innerHTML + " - YouTube";
                    }
                }

                function replaceDescription()
                {
                    var descriptionElement = topWindowDocument.querySelector("meta[name=\"description\"]");
                    if (descriptionElement !== null)
                    {
                        descriptionElement.setAttribute("content", "");
                    }
                }

                removeElements();
                injectHtml();
                replaceTitle();
                replaceDescription();
            });
        }
    }

    topWindow.addEventListener("DOMContentLoaded", removeEventListenerAfterFiring(1, bypassAgeVerification), false);
}(window.console, window.top, window.location));