who rules if the king is too young
Regency Acts According to the Regency Acts in force, if the monarch is under the age of 18 years when he or she succeeds to the Throne, a regency is automatically established, and, until the monarch attains the age of 18 years, the royal functions are discharged by the regent in the name and on behalf of the monarch.
Succession to the French throne Thus, the early Capetians made their position de facto hereditary by associating their eldest sons to the kingship while they still live. By the death of Philip I, this hereditary feature had become established in custom. Even though Philip refused to have his son crowned during his lifetime, Louis succeeded with little trouble. Yet the association of the eldest son to the kingship continued for two more generations, with Philip II Augustus being the last king so crowned.