Board Thread:Manga/@comment-29015168-20160918112018/@comment-27321453-20160923191926

Speculations are that the villagers were turned into Titans by a gaseous form of the Titan serum and the ones in this recent battle were all humans hiding in the bushes who each had a Titan serum syringe and just coordinated their transformation with Zeke's.

Also it seems Zeke can only control the Titans freshly created, those are the ones who also could move at night and the ones we've only seen the Beast Titan around, but I believe he'd be attacked like any other Shifter if he were to encounter older Titans, I mean the ones that have been roaming outside the Walls for decades.