...Is it right to use spoiler tags for animes of this old?
Age doesn't matter when it comes to the definition of a spoiler. You reveal details of the story which can only be obtained by watching it. There're ALWAYS people who don't know the series yet. Besides, if age was a factor, what would be the appropriate limit to call it not a spoiler anymore? 10 years? 15 years? 20 years? You see where this is going...
