This should be in. It would make the game more historical, interesting and fun.
Say an unmarried teen gets the throne. Instead of the vassals starting a war to put some random guy at the throne, the power of the land might instead make a war to force the new king/queen to marry someone politically convenient for said power. Say the under-age queen of France is 15. Then the duke of four duchies starts a war to force the queen to marry the dukes eldest son. I mean, in real life forcing a king, even a new king, to abdicate was illegal and unusual. Normally you tried to instead control the ruler, by means of regency or marriage.
If the player is the one trying to gain power. Nice, a new way to move up in the world.
If the player is the underage ruler. Either he can try to win the war, or he can afterwards plot to kill his new spouse. Maybe some events need to be added to stop unwanted pregnancies (refuses to enter bedchamber).