It's more than just age. Compare it to architecture... Some old buildings are architecturally interesting, or historically interesting - when people look at them they see value. Other old building are just old, not really worth preserving, and of no real interest to anyone (except maybe the people that live inside). Bikes are the same.kujhawk said:
A lot of people will agree that certain bikes are definitely "classic" based on design or impact on the industry. Other bikes will probably have a mixed interest - some will think that they have value, and others will not. And a large number of bikes will likely have sentimental value because they were someone's first bike, but most people would not really consider them "classic."
So depening on the bike, you might get a lot of people to say it's classic, or you might get relatively few. There is no universal definition that can be applied. However, in the end all that matters is that you like the bike that you're riding.