I keg (and drink) beer all of the time at 4 weeks- BUT there are about three-four styles I don't see that happening in. One is a Belgian strong. Others are barleywines, oaked beers, and lagers. Sours, too, of course but I don't make those.
I'm making a tripel in a few weeks, and even though I have room in my kegerator for 5 kegs, I'm going to bottle the tripel. That's definitely a beer that needs some time so that it's not "hot", the ester/phenols are balanced, and the beer has time to condition.
Lots of beer styles can be ready in 4 weeks or less. IPAs, APAs, ambers, English milds, bitters, pale ales, even stouts, often get put on tap at week 3. But I would never even try with a Belgian strong ale.