I can't remember when I started cantering, but I can tell you what I do with students.
If I'm starting with a raw beginner, particularly a child, they absolutely MUST have impeccable balance at halt, walk and trot before they canter. I work with them in 2 -point, no stirrups, standing vertical in the stirrups, no reins, etc.
They must have very good control when riding around the arena on their own, in walk and trot and have an established 'stop, go, turn' button. They must have found their centre of gravity, so their legs aren't swinging wildly around, and they must not still be relying on holding onto the saddle for balance.
I start them on the lunge in canter, just for a few strides at a time and gradually increase the time as the student becomes more confident and balanced.
I am a firm believer in not allowing a person to canter until they have excellent balance in the saddle.