She is not too old for JO, it is my understanding that there is no age limit. But every gym will set their own age limits and expectations. Many gyms do have age limits, mine included so I would like to give you a little background into why I have made that desicion.
One of the most difficult times int he gymnastics journey is the puberty years. At this time kids are growing at a rapid rate and they are far more prone to injury than at any other time. If you,look at the time line for a kid who is 9 or 10, if they start team at this age, then at the time they are going through puberty it will be the same time the hours are increasing, the difficulty level is increasing and the injury risk is increasing. This can be a formula for serious injury. Our aim is to hit that point prior to puberty, so when the girls are going through puberty they are maintaining hours not increasing them to minimise the risks.
The safety of the gymnasts should always be the number 1 priority of the gym. This is not the case in all gyms, just why many gyms make such a ruling.
The other issue is that gymnastics skills are much easier to learn prior to puberty. Once kids hit puberty their body composition can change very quickly and set them back. Fear often sets in and kids have to continually adjust what they are doing as they continue to grow and hit peak height velocity. I know at 9 puberty is usually still a few years away, but if she is just starting Team then her peak skill learning period, when the core basics have been mastered and she is ready to learn significant skills is also a few years away, and it is very, very difficult when these two times clash. Imagine teaching a child the most difficult skills they will ever have to learn right at the same time they start to develop fear and are growing rapidly and having a change in centre of gravity almost each lesson.
The other aspect could also be due to spotting. In the earlier team years there is a lot of spotting to be done. Many if the core skills can only be learned with constant spotting. Once a gymnast reaches a more advanced level this can be reduced as their development has reached a stage where theynhave enough background to be able to learn many skills through drills. This is a big reason why teams start with very young kids. Spotting can cause extreme wear and tear on a coaches body, coaches need to look after their bodies first and foremost as they can't successfully do their job and safety catch children if they are physically hurt. Keeping participants in the early levels under a certain age, so as to ensure they are small enough is a strategy gyms may use to keep their coaches safe.
Again I am not saying this means your daughter is too old, I am simply explaining why many gyms make this desicion. It is rarely about scoring well, because older participants often score better. Many have smaller divisions so are more likely to win and are better able to put the finishing touches on their routines when they are older that give them higher scores.