Not really. Usually the girls are married once they bleed for the first time, and young rulers/generals do not lead themselves the armies or realms - they are aided by councils and tutors. In my own version of AGOT, I make the marriageable age 14 and adulthood 18.
Also, in CK2, the marriageable age represents the age where they will have children. It is highly unlikely to be able to have children at 9, as far as I'm aware (unless the reproductive system has been forcefully activated, if you get what I mean). If we put the marriageable age at 1, for example, the engine will think they can have children already.