No opinion on the age of a GM. I think that it is really a matter of maturity and not of age. Also, being a GM usually involves running a school or multiple schools. Doing that well is a different set of skills than that of technical proficiency in the art.
Comparing a GM who is younger than what is typical to a child with a black belt is a red herring. Let's say that a child gets his first pum at five (like the kid in that ATA thread). He can test through fourth pum prior to turning fifteen and a fourth pum can convert to a fourth dan when he is 18 (if I am reading article 8 correctly http://www.kukkiwon.or.kr/viewfront/eng/promotion/regulations.jsp). Not entirely sure, as on the same page, it indicates that a fourth dan must be 21.
Anyway, if it's 18, then by this time, this fourth dan has been practicing since he was three or four, so you are looking at like fourteen years of practice. If its 21, then he's been practicing for about seventeen years.
Same kid test for his fifth dan at 25 then his sixth at 30. That is 26 years of practice. I'm not sure if sixth or seventh or higher is called grand master, but with 26 years in the art, an in this hypothetical scenario, our hypothetical kid has been practicing for an actual 26 years and has taken no breaks in training.
I'd certainly consider him my senior and would consider him to be an inspiration. Should he be called a grand master? I don't know.
I think that it is more important to look at what kind of person he or she is than what their title is.
Comparing a GM who is younger than what is typical to a child with a black belt is a red herring. Let's say that a child gets his first pum at five (like the kid in that ATA thread). He can test through fourth pum prior to turning fifteen and a fourth pum can convert to a fourth dan when he is 18 (if I am reading article 8 correctly http://www.kukkiwon.or.kr/viewfront/eng/promotion/regulations.jsp). Not entirely sure, as on the same page, it indicates that a fourth dan must be 21.
Anyway, if it's 18, then by this time, this fourth dan has been practicing since he was three or four, so you are looking at like fourteen years of practice. If its 21, then he's been practicing for about seventeen years.
Same kid test for his fifth dan at 25 then his sixth at 30. That is 26 years of practice. I'm not sure if sixth or seventh or higher is called grand master, but with 26 years in the art, an in this hypothetical scenario, our hypothetical kid has been practicing for an actual 26 years and has taken no breaks in training.
I'd certainly consider him my senior and would consider him to be an inspiration. Should he be called a grand master? I don't know.
I think that it is more important to look at what kind of person he or she is than what their title is.