I'd say the age is less important than things like how good it is, how well the plot hangs together and how good the acting is. The oldest films on IMDB are from 1888 and feature bits of Leeds (http://www.imdb.com/title/tt0392728/ and http://www.imdb.com/title/tt0343112/, or http://uk.youtube.com/watch?v=L7saH58usq4 and http://uk.youtube.com/watch?v=F1i40rnpOsA on Youtube). They're obviously historically significant but they probably wouldn't feature in someone's top 10 list of classic films. Of course there's the question of what "classic" means as well.....