Does cinnnamon have an expiration date?
If you buy ready ground cinnamon, there may well be an expiry date on the jar. This doesn't mean that cinammon past this date is actually dangerous, but it will lose a lot of strength and flavour over time. With many spices, if they are kept for a long time, without actually becoming harmful they will reach a point where there is no point in using them, and some can even start to taste unpleasant.
Some studies suggest that ground cinammon loses much of its effectiveness after about 6 months, though the recommended shelf life is more like two years. A lot depends on how it is stored: if it is kept in a sealed container in a dark, dry and cool place, with no contact with heat or damp, it will keep fresh for much longer. A cinnamon stick can be kept for longer.
You can find information about storing ground cinammon here; however, for a really fresh taste you should grind your own spices whenever possible.