Maturity and longevity?

[RyanH]

Ok, what's the great secret to knowing how long a wine will keep and/or when it will reach its peak? Sometimes I've seen wines refered to as being good for only a couple of years. Other times I've seen reference to maturation decades away. But how these people got that information I have no idea.

So as I'm browsing the shelves , be it at the store or online, how can I tell if I'm looking at a wine that should (or could) be cellared for 20 years, or one that I should uncork in a matter of months?