He looks frail here and noticeably underweight. Combine that with his age of 12 and it’s no surprise that he looks frail. This is a purebred cat if he is a genuine Russian Blue. It is sad to see such a fine cat in this condition.
Note: Some older videos on this page were hosted on Vimeo. That account has now been retired, so a few video blocks may appear blank. Thanks for understanding — there’s still plenty of cat content to enjoy!