How old does an anime need to be before it can be called a classic?

[Star_Of_Hope]

So, what do you guys think?
Do you think it needs to be too old with some cultural aspects embedded in it, for it to be a classic, in some distant future.

 

[Blackangel]

not sure lol
ant may be a decade or two will do the trick but i can't be very sue when it comes to classic anime.