Sheng PuErh can be kept for more than hundred years whereas Shu PuErh is deemed to be at it best between ten and twenty years old depending on quality. These can be kept longer but experts feel that the tea doesn't continue to improve after this time. As a rule of thumb the higher the quality of either type, the longer it can be kept. The easiest PuErh teas to source are usually those that are between one and five years old.
PuErh tea is stored very differently from green tea such as Long Jing and light QingXiang Oolong which should be kept in air tight containers and ideally in low temperatures. PuEr tea should be stored in a stable environment that is not subject to sudden changes. Ideally dark, warm/frost free and in an environment where there is a natural, seasonal changes in humidity that encourages the enzymes that produce the secondary fermentation, and so the ageing of the tea. It said that places located round the Tropic of Capricorn, such as Singapore, Hong Kong & other Southern Chinese provinces are the best.
Although it is beneficial for PuErh tea to be exposed to humidity, this should not be for extended periods of time i.e. years. This will cause the tea to spoil and potential become mouldy. By providing an environment where there four natural seasons the tea has a chance to age during the moister summer seasons, then rest and dry during the winter. On the other hand, too drier conditions will mean the tea dries too slowly and will take considerably longer to mature.