While my views on this are 'evolving', where I come down on this now (being a level 157 Industrial) is this:
*There is no reason anymore to stay in Global any longer than is necessary to upgrade troops in preparation of loss of Industrial opponents. Global is now the 'lost' age in the game. It has been all but totally absorbed into Atomic. Even 'maxers' have no reason to not rush to Atomic once core troops are upgraded (by the way, this puts the motivation for the level 220 CWA requirement in a somewhat odd light, since it was meant to reduce content rushing).
*The silo should be among the first builds in Global, however the protection afforded by Silo is not 100%. Being in Industrial gives a shield against top players that is 100% effective.
*Enlightenment and Industrial are the two ages with the strongest cases for maxing for reasons both pragmatic and pedagogical. Enlightenment in order to correct dislocations from prior rushing (and learn a solid ground attack) and Industrial to take full advantage of the shield against top players (and to learn how to use and not lose airplanes while they're still cheap). If you can stomach maxing for a few months (not including University and Generals however) then these are the two ages to do it. If you can wait even longer and put in extra University time, Industrial is the time to do it. After that it's a race to 220 or should I say a marathon.