Maybe that is because of the kids who are doing MP's Tr's and GR's. See the thig is that sometimes is is very hard to make a group af all the kids who are 12 years old. Thas why, maybe some kids who arent ready enough to compete in age group1 can still compete with their friends who are 10-11 years old.
Regarding the national development 9-11 idea is not bad, however the people who were prepering the rules (working group mainly involved in FIG Aerobic Academies) might have a better idea why that is 10-12 and 12-14.
I think we will have more answers to all the questions after 20th of January, when the intercontinental judges course will be over and answers answered.
robert