I spent hours trying to solve this problem on my own, using search engines and surfing the massive Google+ and Youtube interface. All of the solutions I found via google search were years old, and they all mentioned the same "sign out of all other sessions" option in gmail and youtube, both sites of which seem to no longer have this option. The customer service telephone number failed me for a solution as well, as did the support section of google.com; and, the user activity section in gmail showed that no other IPs had logged into my account. I have literally exhausted myself trying to come up with an answer.
The reason I need this option is because I have had suspicious Youtube watch history for months now, and it's finally starting to irritate me. I'd like to keep my Youtube activity private, and these random strings of videos I find in my history leads me to believe that someone is logged into my account from another computer or mobile device. Most of the videos point to a user that is at least my father's age, or older... and if it's an older family member, I'd rather not them have the ability to view my watch history, for obvious reasons; so, if someone could please tell me how I can go about kicking all other devices off my Google+ and Youtube account, I would be sincerely greatful. Thank you.