Like Most Things...
If you wait long enough, someone else will do it.
Happily, Joseph and Peter, neither of whom can stand their hair growing long enough to touch the top of their ears, are now able to cut each other's hair.
My job: enter room littered with freshly buzzed hair and sculpt the final touches around the ears, neck, and forehead. Vacuum (floor, not boys... usually). Repeat.
I like this new stage of independence!