Is it possible to determine the age of a building by just looking at its window?
This is but an urban legend. Glass does not get thicker at the bottom. (Sure, glass is fluid to some tiny extent, and it can be demonstrated, but not in this way.) It is just that the glass panes were initially manufactured with uneven thickness. Then the people who stuck the glass into the frames would orient the thicker side down, maybe because it is more stable this way, or because it feels right, or just to mess with us. Sometimes they didn't pay attention and turned it randomly.

Supporting links: 1, 2.