Get them while the're young,
The only cases so young people are sent to war is when there isn't enough manpower in the ranks. In this case we have 80.000 people vs 100.000 drones.
Heck, they need to enlist the kindergardens as well
And I sure hope there are no women in those 80.000 because as we all know they are completely useless in the Narutoverse. Other than being used as breeding machines for the next look-like-their-fathers generation that is.
Madara sure knew what he was doing by not having to tolerate 100.000 women for 20 years in order to create such an army