Most airports have Elite Flyers lines (Plat, Gold, Silver with their respected airlines), plus Clear - which is fabulous. Both of these get those passengers who do travel alot or pay for it through security very quickly. Also, wheelchairs and special assist passengers get a "go to the front" of the line free pass most places. I don't see any reason to further break down boarding. As mentioned, it may help at some airports and hinder at others. I also will agree that kids can either take lots of extra time or be quicker than some adults, just depending on how their parents have prepared them. TSA has some great family tips at TSA: Traveling with Children , along with several other pages to help all travelers figure out how to pack, travel, check-in and basically make their air travel easier and safer.
Jan '07 Pop Century, Mar '07 Day Trip, April '07 Off Property, May '07 OKW, July '07 POR, Oct '07 Pop Century (& MNSSHP!!!), Dec '07 Day Trip
Jan '08 POR
Feb '08 Pop
Mar '08 Off Property
April '08 AS Sports - I think - still gotta book it