In reply to Malt_Loaf:
Oh, crikey. Anything I write now is going to be massive generalisation, and anyone who knows anything about wine will be able to shoot holes in it.
But: in order of needing more time in bottle to become mature, red > white. Within red, Bordeaux > Rhone > Burgundy, Chianti, Nebbiolo > Rioja > Beaujolais, and French country variants like Corbieres or similar.
To look at Bordeaux in particular, you've got the right-bank (Merlot dominated) wines from St Emilion and Pomerol, and the left-bank (Cab Sauv) dominated wines from the Medoc and Graves. And also lots from between the two rivers (Entre-deux-mares, Cotes de Bordeaux, etc) which might try to ape either style. Typically the merlot wines will come around quicker than the cab sauv.
What you are looking for is some sort of balance between tannins, acidity, and fruit. Very roughly the tannins will dominate at first, and recede after some time (which can be enormously variable). So you are looking to catch it when the tannins have died back anough to let the fruit through, but not too far. For wines designed to be drunk early this might be a few years. I have stuff in the cellar I wouldn't dream of opening this side of 2030.
Problem is, the fruit also dies back. The tannin does get replaced by some complicated tertiary flavours, which some people love and some don't.
One of the best things about the wine society - they give you a drinking window for each bottle so you know what to experiment with!
Decanting - yes, this can definitely solve some of the early-drinking issues. For a youngish bordeaux I'd be looking at 4-8 hours in decanter.
Cheers
J