It really depends on the type of beer, the gravity of the beer, the type of fermentables in it, and any issues that cropped up during brewing and fermentation.
There's really no hard and fast rules, but bigger beers generally need more time to condition, ut just about every beer, will have a window of greeness that it needs to pass through before it is truly ready.
But taste is subjective, plenty of brewers, especially those starting out drink plenty of beer that other's would deem green and enjoy it. It usually only when a brewer is not happy with a taste in their beer, do we then ask how long it has been in the bottle, and usually it turns out that they are drinking really young or "green" beer, and 99% of the time they give their beer a couple more weeks, and come back to us reporting that NOW the beer tastes great.
Stouts and porters have taken me between 6 and 8 weeks to carb up and condition, and I have a 1.090 Belgian strong that took three months
to carb up, but still needed another 6 months to lose the hot alcohol harsness.
More info can be found here....Revvy's Blog, Of Patience and Bottle Conditioning.
I also have been collecting stories of extreme cases of letting beer age a long time to clear up on some really troublesome brews, to basically stop newer brewers from committing beericide and dumping out beers that are more than likely just green.
Hope this helps.