I don't know the scientific info on it, but I can tell you what the tea
bosses around here say.

Tie Guan Yin, about a year. The freshness is a deciding factor on what
the final price will be at market, and anything over a year is
relatively worthless.

Wulong, strange. There are some types of Wulong that are better if
they have been aged, apparently. Generally, the Taiwan Wulongs will
last for about a year before they are too old.

Green, two years.

Pu'er, the elder the better.

Keep in mind, this is from some bosses who are hardly scientists; some
of who are hardly honest. heh.