i was ten, and it was a huge "rite of passage", and i am very anti-piercing small children.
that said, i have seen little boys with pierced ears, and i don't like that, either.
the only little boys i've ever seen with pierced ears were somewhat unkempt looking though- long scraggly hair (i am not anti-long hair on boys - my son had pretty long hippiesh hair, because his curls were so gorgeous :)) but did not look like his parents were taking the best care of him...so to me that is the stereotype. now if it was a well cared-for clean little boy it would be different..i'd probably still feel the same, but i'd feel guilty about judging lol.
(eta- i have had five piercings in my ears, from when i was younger. i only use the 2 now, and yes, i have three scars/marks on my ears. it was fun to have them in my 20's, but now, i don't say i regret doing it, but i do wish i didn't have marks on my ears from them. i wouldn't ever do that to a small child- not my body, not my choice.)