@boomerang,
Maybe osso's line of thinking has merit.
He is 10 years of age, has been allowed to have blue hair, green hair, I get that, Individuality, being himself, but... Mo's Mother had a piercing in her eyebrow? Maybe he (Mo) was ridiculed at school for that, that's "un-usual" for a parent, not for a teenager... Maybe, he's put the breaks on, has a problem communicating with you about his logic, and that being, he's only 10, nearly 11...It's not an Adult decision it's a whole in his body, sure that may close up, but it also may send out a signal of "tough" .
Maybe he knows you think if he doesn't he will be a rebel later, that's your fear yet, he purely wants to be responsible for now, like when you are old enough to make that decision for yourself.
I do think he's a little young.
It's like an 11 year old girl saying, I want my uniform shorter, way up high and I want to wear mascara to school...at ....11....
Does his mates have earings? Colour their hair?