Resolved Question: How long does loose tea least?

I found a tin of Oolong tea in the cupboard and made a pot.
It was VERY good. I must have had the tin for a number of years.
How long does tea stay brewable if kept dry, cool, and sealed in a box?
I have heard that some Pu-erh teas are more than 80 years old, just for an extreme example.

Thanks!