I turned blackbelt at Tae Kwon Do when I was 10. I have the certificate to prove it too. Also, the master who graded me was from Korea, which is to my knowledge, where TKD originated, so I would think that's an achievement.
I'm 13 atm, 2nd dan black belt. Btw, TKD goes:
Blackbelt
1st dan blackbelt
2nd dan blackbelt
Not like Toribash where it goes blackbelt to 2nd dan.