I lived in Korea for a few years and during my first year there, I trained 5 nights per week for about 10.5 months (minus about 5 weeks of missed training due to tearing 3 ligaments in my ankle) and was allowed to grade for my black belt!!! within a year!!!
I have a background in Karate (3.5 years, 1st kyu before starting TKD) which helped me pick up the style quickly... but like another poster mentioned earlier, a black belt grading in Korea is not considered mastery of the art at all... it's probably not until you are 4th dan that you are considered to be experienced.
It's interesting to note that most men in Korea have achieved a black belt in TKD due to the mandatory military service requirements and the training they undertake.
Also, the requirements for the black belt grading were ridiculously simple... the whole grading took about 5 minutes from start to finish. I was still disappointed, despite having watched black belt gradings prior to my test.
I could've gone for my second dan before I left Korea earlier this year, but I just didn't feel deserving of it.
Still, I console myself with the knowledge that I was able to achieve what I did without a word of English being spoken EVER and by training VERY hard every night for about 1.5 hours. I miss those days
The TKD schools in Korea are predominantly money spinners and it's standard for a person to get to a black belt ranking within a year, regardless of how well or how poorly they are performing. I've yet to meet someone who failed a test in TKD in Korea!!!
I also miss how they have these big yellow vans in Korea to pick you up and drop you off after class as part of your monthly training fee. Man, I'd love to see some of those in Australia