A tablespoon is a non-scientific but very widely used unit of volume, which works very well in cooking, herbal medicine, etc. It is represented by a capacity of one tablespoon which varies from roughly 15 mL in the US to 20 mL in Australia.
1 If tea is properly stored, it can potentially last up to a year for green and black teas. White tea lasts about six months before it isn't as good in quality as when fresher. Stale tea (or bad tea) will taste flat, as if you're drinking paper.  Glass or ceramic containers are fine provided that they're opaque.
If you're talking about loose-leaf tea that has been properly stored (in a dry area), then no. Tea starts to break down and lose flavor, but it generally does not spoil. If you have tea that has been stored for a very long time, it will often taste very bland, and it may develop off aromas. But it is generally not harmful, unless it has been stored improperly (such as in too damp an area) and has grown mold.