Carlos I , Felipe IV and Alfonso XII of Spain were not minors when they became Kings. At that time, the majority was at 16 yo.
Who was the last in each of the following royal houses (both reigning and non-reigning) --
Some off the top of my head:
England: Ethelred II, Henry III, Edward III, Richard II, Henry VI, Edward V, Edward VI.
Scotland: James V, Mary Queen of Scots,James VI.
France: Louis IV, Louis IX, Jean I, Charles VI, Charles VIII, Francois II, Charles IX, Louis XIII, Louis XIV, Louis XV.
Spain: Juan II of Castile, Carlos I, Felipe IV, Carlos II, Isabel II, Alfonso XII, Alfonso XIII.
Russia: Ivan IV, Mikhail I, Alexei I, Ivan V, Peter I, Peter II, Ivan VI.
Sweden: Christina, Carl XI, Carl XII.
Netherlands: Stadholder Willem III (William III of England), Wilhelmina.
Portugal: Afonso V, Sebastian, Maria II.