There are many adult bullies, and while I'm not sure if they were also bullies when they were kids it's certainly not the case that it's necessarily a temporary

There are many adult bullies, and while I'm not sure if they were also bullies when they were kids it's certainly not the case that it's necessarily a temporary stage of someone's development. Adult bullies tend to operate quite differently, though, and can be much smarter about plausible deniability.