It varies on the style really. In general terms, the darker the beer, OR the more hops used, OR the higher the alcohol content...increases the shelf life and stability.
That's why you see aged and oaked Stout beers...however a kolsch or hefe or a wit should be drank fairly young. Same reason Bud/Miller/Coors wants to show off how young their ultra-delicate 'beers' are.
So the light beers will lose their peak flavor sooner, but woudl still be drinkable at 1 year. my kegs last months and month and months usually too.