Not a long ago, Google removed Opera/Presto support and blocked proper functioning of their web sites in Opera 12. But if you set a proper masking you can get the most of Google's resources working in Opera 12 again!
Use this instruction: https://forums.opera.com/topic/5577/new-youtube-problems-with-opera-12-17/32
Also, add the user-agent masking for "google.com" by editing override.ini and using this custom User-Agent string: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0 Opera 12.16
And you'll get:
Working Youtube's comments (displaying and commenting)
Working Plus.google.com portal
Valid google search engine (instead of simplified half-functional design) with the most of functions working (such as "find similar image") again.
Thanks, that fixed YT at least, but it broke paypal. I guess i will finally have to move out of opera.