Which teas age, and why
Raw pu-erh ages because it was sun-dried, which leaves enzyme and microbial activity intact where machine drying would have finished it. White tea ages because minimal processing leaves plenty for time to work on. Traditionally roasted oolong ages because oxidation and real charcoal roast give it the structure to survive years. Green tea, most black tea and lightly roasted modern oolong do not age — there is nothing in them to develop into, and what happens instead is that the aromatics fade.
What changes
Across all three ageing categories the direction is similar: fresh, bright and floral notes recede; dried fruit, wood, camphor and a thick sweetness arrive; and the body gets noticeably heavier. Young sheng pu-erh’s severe bitterness converts into depth over fifteen years or more. Aged white tea moves from hay and melon to dried date and honey. Aged oolong loses its floral top notes entirely and turns medicinal.
Conditions, and the one that differs by category
Dry, dark, stable and away from odours applies to everything. The exception is airflow: white tea and roasted oolong want to be sealed, while pu-erh must breathe, because sealing raw pu-erh airtight stops the microbial activity the whole exercise depends on. A cardboard box in a stable room is a perfectly respectable pu-erh store and is what a great deal of collection storage actually is.
Ageing is not passive for every category
Aged oolong needs maintenance. Finished tea reabsorbs atmospheric moisture, which dulls it, so traditionally roasted oolong is re-fired lightly every few years to drive the moisture off. Neglect it and the tea turns sour rather than deep. White tea and pu-erh need no such intervention, which makes them the easier categories to start with.
What can go wrong
Damp is the main risk and it does not produce maturity, it produces mustiness. Odour absorption is the second: tea takes on kitchen smells over years and there is no recovering from it. And the third is buying age rather than storage — a cake stored badly for twenty years is worse than the same cake fresh, and pressing dates on wrappers are claims rather than proofs.