There is no hard and fast rule about aging. Some beers benefit from it, some don't. Ultimately it comes down to what your own tatse buds tell you.
In addition to following your taste buds, which is the #1 thing I would recommend, too, consider the beer and how you made it.
Aging doesn't fix all mistakes, of course, but it can help mitigate them.
A properly made ale with a "normal" OG can be ready to drink very soon. But even a properly made barley wine might be best in 9 months.
But if the yeast is underpitched, or the fermentation temperature is too high, or the beer has some undesired harshness, those are the mistakes that very well may improve with some aging. Of course, if you don't make those mistakes, you don't have to age out off-flavors.
I have one "normal" ale that needs a bit more aging than my others (mostly pale ales and IPAs and hoppy ambers). My oatmeal stout needs a couple of weeks longer for the flavors to meld and blend and for the roastiness to subside to a nice beer. My typical fermentation schedule for most ales is 10-14 days in the fermenter, dryhop 3-5 days (if doing), then into the keg. I do the same with the stout, but let it sit about two weeks. Then it goes into the kegerator with the others.