I'm not a native, so I think you should rely on the other answers. But, I noticed that this is a problem of collocation. In this case, I can suggest you to check this website out: http://www.ozdic.com/collocation-dictionary/clothes Everytime I'm not sure about what adjective is commonly used with a particular word, I look it up on this website. Hope that helps you. =]

Yes, classic clothes is the correct term. A navy blue blazer for men is one example. A little black dress for ladies is another. Classic clothes are styles which are timeless, which do not go out of fashion after one season, which work well for you year after year.

Yes, we can say classic clothes.

Typically, the term would be "old clothes" if it is old. Or "out of style" if you believe that they should be burned since they are so old :D