In the movie The Emperor’s New Groove, Kuzco is confirmed to be 17 (turned 18). That’s kind of young to be emperor. And it seems like he’s been emperor for a while now. Where are his parents though? In the TV spin-off The Emperor’s New School Kuzco’s dad, the former emperor, disappeared at sea while Kuzco was still a baby and it is confirmed that Kuzco inherited the throne at that point. This can be further confirmed in the flashback scene in the movie where we see Kuzco as a baby. He is wearing a crown, which is exactly the same as his grown up self’s and his father’s. Now this could be just a joke towards Kuzco’s royalty, but wouldn’t they have used a different crown instead of one that looked just like an emperor’s crown?
Kuzco becoming emperor as a baby would actually be a safe bet historically. Throughout the world’s history. there have been plenty of monarchs from all over who were crowned while they were children, some when they were still in the cradle (Henry VI of England, Mary Queen of Scots, Emperor Shang of Han dynasty China, Shah Shupar II of the Sassinid Empire, etc.). In all kingdoms and empires, when it came to lineage, when a monarch would die the throne would go to the nearest of kin, which ideally would be the original monarch’s child. There were no age limits on the title of monarch. So it would be safe to assume that the Incan empire would be no different and would crown Kuzco as emperor while he is a baby.
Kuzco becoming emperor as a baby would also play a big part in Yzma’s story. In the case of when a child would become monarch, a regent would also be put in place. As a child cannot actually rule, royal governments would have the child’s regent act in their place until the child became old enough to rule on their own. Most of the time the title of regent would go to the child’s surviving parent (most of the time the mother) or someone else chosen by the original monarch or the government. In Kuzco’s case, his mother is never mentioned in canon or seen so it would be safe to believe that she is out of the picture when he takes the throne. Because of this it is likely Yzma was the one who is appointed regent as she is the Emperor’s advisor and she herself mentions in the movie that she raised him. Also in the movie it seems as if she has had experience in running the empire to the point of it being a habit.
Also in the case of young monarchs there is what is called a majority age. It is at this age that the monarch becomes a fully independent monarch and therefore there is no need for a regent anymore. In some monarchies the majority age is 18, which is the age Kuzco turns in the movie. So in the movie Kuzco is now able to act as sole monarch and thus Yzma’s power would be cut back after years of acting as regent. Now, this probably would not go down so easily for her hence her meddling in government and parading herself as the empress. This also gives us further insight in Kuzco’s annoyance towards her doing so as he is now legally an independent monarch and he does not need Yzma ruling in his place anymore.
So far this seems to be accepted as canon and I thought I would just throw it out there for anybody who is having questions and whatnot.
P.S: Bonus theory time. You know the whole ‘no touchy’ thing that Kuzco does (lol)? It could either be because he simply does not like being touched or because of another royal tradition. In kingdoms and empires, it is commonly believed that monarchs are blessed by gods and they are thus seen as holy in a way. It is because of this belief that they are literally untouchable, as in it would be even illegal to touch a monarch without their consent. This would explain Kuzco’s ‘no touchy’ rule.