Questions About the Noxian Army and the Trifarian Legion

Basically, I know that you can get conscripted at a very young age. Darius, Draven, and Quilletta were but just because you can doesn't necessarily mean you will. So at what age does the Noxian army consider is standard for enlisting or conscripting into the army? And a follow up to that, at what age do Noxian soldiers who have proved themselves get selected to join the Trifarian Legion? I understand that there isn't a set age per say as it is by merit that the selection process is made but is there an average?

If a Rioter could answer this, I would be eternally grateful Say this in a Toy Story Alien voice