It really depends on the beer, but I'm with whatsleftofyou- most of my IPAs are best as soon as they are carbed up.
Some IPAs might be a bit better later on- maybe something that is very bitter, for example, or something loaded with late addition chinook hops, which can be harsh young. But most medium-IBU medium OG IPAs have the best hops aroma and flavor when they are fresh.
Keep in mind that an 8 week old IPA is still pretty young, though! When we talk about drinking them young, that's still not "aged". Two weeks after bottling may be a bit too young, if the beer hasn't had time to clear yet. But anytime from bottling up to about 12 weeks old I would consider a good time to drink an IPA.