Not to repost the same question all over the place already, but I recently saw this post on Mental Floss about what the oldest thing you own is. Liza, who posed the question originally, listed her page from an illuminated manuscript c. 1450. Chris Higgins, who posed the question again on the Mental Floss blog, noted the oldest thing he owned was a wprint probably from the 1950s....but even more he realized most of his belongings were no older than the 90s. This is the part that I think is most interesting. He also questions what is the oldest thing you own that you use regularly! I think a lot of people have old stuff chucked somewhere, but not really in use. He thought probably his apartment was truly the oldest thing he used regularly (1917).
The one thing I don't think either of them have touched on that interests me is how have the old things you own and use changed since you got them? I wonder if the more they change the more attached you become to them. See also Khoi Vinh and my post on patina.
I think the oldest things I own must be a children's book (Wizard of Oz or Waterbabies perhaps) or a piece of furniture, but I don't have dates on any of that stuff handy, or at all on furniture, and I've never been really bothered to find out. Definitely no books from 1450 in my collection!