I just got a series 1957 one dollar bill in change at the drug store.  Aren’t bills supposed to be retired once they reach a certain age?  This thing is so old it’s very noticably different in appearance than the dollar bills I’m used to seeing.

UPDATE: Due to reader demand, I’ve scanned the dollar bill in question, alongside a 2003 dollar bill for comparison.  The 2003 is on the top; the 1957 is on the bottom.  The back of the bill looks the same as current bills.