Types

There are four main types of white tea, ranked by amount of buds.

1. Silver Needle, all buds
2. Baimudan aka White Peony, buds with leaf
3. Shou Mei, all leaf

Silver Needle is all buds, so highest grade.
But Shou Mei become valuable as it ages.
~ Beto

As of May 1, 2018, the term Gong Mei specifically refers to teas of the Xiao Cai variety.

Historically, Gong Mei used to mean a grade that had more buds than Shou Mei which typically has more larger leaf/lesser grade leaf to bud ratio. It is still sometimes used incorrectly to mean such.

Aging

1 year tea,
3 years medicine,
7 years treasure.
~ Chinese Saying

Aging “lower grade” white tea is a common practice. I see teas sold at around the 5 or 6 year mark. At 7 years, a tea is considered an old white tea.

The color of a good aged white tea liquor is like amber, bright and oily; its taste is full, the mouth is smoother, and the sweetness and viscosity will gradually increase.
~ A Questionably Translated Website

The white tea used for aging is usually Gong Mei or Shou Mei, since they are mostly fully formed leaves. I have seen aged Baimudan, but it seems Silver Needle is rarely aged. Silver Needle is limited in production and sells immediately.

Tastes great when they mix blends, but wrap your shit up to age it.
~ Michael Angelo

Storage for white teas matters a lot. Ideally, want to keep it airtight in a cool and dark environment. It will still slowly oxidize in this environment.

Oxidization deepens the flavor and changes its aroma profile. Some of the grassy, floral notes fade, and richer flavors like jujube and fig start to show up. And the texture gets thicker, with more body.