This led me to bring up the idea of the wizard's indenture with Evelyn, a fellow law student who has made her first foray into the world of pen and paper with us recently. Her response was, of course, that selling off young children to go and live with lonesome intellectuals in towers was generally a rather unpleasant reality of the 10th Age... which caused me to examine my own motives for establishing such a system, even in a fantastical (and not particularly pleasant) world.
Here are the forces that lead wizards to be shaped as they are...
BUT FIRST: There are no contracts of indenture. I felt like I should get this out of the way first. Contract law is only developed enough to produce chirographs in the Empire, and as it stands wizards hunting for apprentices generally pass through many lands not their own before finding a child suitable to be raised. They have a simple approach: pay off the parents with a load of gold, then disappear to raise the child in some foreign land.
Wizards build towers. This is so self-evident that it's become an axiom in Atva-Arunia. That is: wizards are isolationist by their nature. They do not like to be involved in the outside world save where it may affect their studies. The tower is the traditional sign of wizardry partly, yes, because it is phallic and many wizards are male, but also because it represents a withdrawal from society. Wizards are incapable of holding together in cohesive groups for any length of time. Why is this, you ask? I will tell you:
Wizards are scholars and academics. But they are also ANTI-ACADEMICS. Where academics want to share things with each other and comment on each other's work, wizards want to learn things and hide that learning from the world. Worse, they are beset by the perpetual bugaboos of academics the world over—overweening pride, intellectual hubris, and prima ballerina syndrome. Unlike the vociferous and easily offended academics of the monastery or the temple-school, wizards are in a unique position: when they disagree with each other, they can literally set each other on fire. Even minor disagreements can become deadly argument. The line between verbal attack and verbal attack is very thin for a wizard.
Furthermore, wizards universally have trust issues. Power is nice, but it also precludes them from having normal relationships with other people. Two wizards cannot have a romantic relationship, for example, because of the lingering fear that one will try to kill the other for access to their books. A wizard cannot have a relationship with a non-wizard because they are simply not on the same playing field. Of course, rare individual instances of these things happen... but on the whole, wizards cannot date, marry, or have children with each other or any one else as a function of their inability to trust and adhere in groups.
So what about this lifestyle makes it appropriate to buy apprentices? Well, though it is the simple perpetuation of a cycle of mild child abuse by many wizards, there are those who treat their apprentices well and seek to prevent the awful treatment they themselves received as children and not carry it forward onto their own apprentices.
The long and short of the matter is that apprentices are wizards' existential and intellectual children. They inherit the magic of the wizard. They inherit the tower of the wizard. They are, in all ways, children of choice. But, as in all other places, wizards must be wary of their timing. If they raise an apprentice who is too readily handy with magic and prepared to take over the wizards' house and libraries too early, the wizard will not be ready for "retirement" and this will essentially be an apprentice-murders-master situation. Likewise, if the apprentice isn't ready but the wizard dies, that apprentice's lifespan just got exponentially shorter because whatever came after their master is likely going to come after them, as well.
These are the beats I was seeking to hit with apprenticeship.
Because this is a fantasy world, it allows me to dwell on certain emotionally real aspects of human behavior. But further, it also allows us to envision a society where things aren't the way they are here. No one really has a problem with the apprenticeship model in the 10th Age. Magic takes 10+ years to learn, and children must begin early if they aren't to have bad habits. Indeed, they are often taught logic and rhetoric before even beginning their central curriculum.
Perhaps this is simply the price of spellcraft.