The oldest items of clothing that I have are three vintage dresses from the 1940's. Two are sundresses and the other is a "garden" dress which was intended for formal parties.
I found them in a vintage clothing shop a few months ago when I was searching for an outfit for a Ya-Ya Sisterhood party that one of my sorority sisters was throwing. They are all in good condition and they fit perfectly -- which surprised me because, according to the owner of the shop, women were typically smaller back then. I loved all of the dresses, couldn't decide between them, and ended up purchasing all three.