Subject: Quoting the Wiki...
Author:
Posted on: 2012-03-19 19:46:00 UTC
The usual recruitment age is 15, as I already said.
However, "Agents as young as twelve aren't unheard of", meaning that in some cases Agents as young as twelve are put on the field. Probably as a countermeasure to the PPC's perennial understaffing problem.
So, we can probably say "between 12 and 15, depending on how much likely is the recruit to survive at least one mission and how much the PPC is understaffed at the moment"