From my previous research we can see that the founding master's of the various Kai-ha, received their 8th and 9th dan in their mid thirties to late forties, and 10th Dan in their fifties. This is in contrast to the later model where 10th Dan was moved up to the age of Seventy. It seems that in the beginning of the ranking system that it was skill not age that determined the level of rank.
If you take a look at the standard time in grade requirements and the hardline stance that Shodan could not be issued until the age of 18, here is what you come up with.
Rank
|
Minimum Time in Grade
|
Minimum Age
|
Shodan
|
N/A
|
18
|
Nidan
|
1 year
|
19
|
Sandan
|
2 years
|
21
|
Yondan
|
3 years
|
24
|
Godan
|
4 years
|
28
|
Rokudan
|
5 years
|
33
|
Nanadan
|
6 years
|
39
|
Hachidan
|
7 years
|
46
|
Kudan
|
8 years
|
54
|
Judan
|
9 years
|
63
|
If you go with the newer model that allows adult Shodan at the age of 16, then it changes the whole thing.
This is based of of the commonly accepted time in grade models. So what if you have a 50 year old that has 45 years of training? What rank should he or she be?
It is a conundrum