I am stuck on the Rival's Quest 26, which is "recruit 5 units from the previous age". How is that actually done? Does a regular building/event building/Special Building produce them? Or is there simply no alternative other than storing buildings to make space in our city to erect a military building from the previous age and then wait 17 hours for it to be built, and then wait for it to make all the individual units? That seems like a *very* long-winded way to achieve the quest, and would actually take longer than the Rival Quest is up for. So how are other players solving this?
There are only 2 ways to do this, in a reasonably short time frame.
1) have an Alcatraz and place a military building from the build menu for the age directly previous to your current, and then collect Alcatraz. You don't have to wait for barracks to build, Alcatraz makes troops from any barracks in your town regardless of being built or connected to 2-lane roads, it ignores all that.
2) The other way is look in your inventory for any previously stored event buildings that also make troops that you may have left in the previous age. Long ago, I left some Knights pavilions in my previous age and I could build them from storage, finish special production on them, self-aid them, and collect until I get 5 (knights pavilion only makes 2 at a time.)
Or as you say, you're kind of screwed if you have to do it the long way, build previous barracks, you'll need 2 if you want to train 5 units without using diamonds to open the 5th slot, and wait anywhere from 10-15 hours for the barracks to build, then wait another 4 hours after the barracks build to make the troops. Or of course you can throw diamonds at all those waiting times to rush it. You can bet that diamond option was the point of this quest.
There are downgrade kits coming soon to revert a building to a previous age or reverts them to bronze age, I don't know, I don't have any yet and I haven't seen them in the game. Edit: Also I found the downgrade kits, one-age-down and revert-to-bronze-age are indeed in the Silver and Gold passes for this event, behind a nice pay wall. If you weren't foresighted enough to save a building in a previous age in your inventory somewhere, that's what you would need to send one of the many event buildings that make troops back to a previous age so that it works for the quest.