I feel this has shifted to be a bit older with time. My older DD had just turned 9 the day of the first meet of the season when she did level 7 in 2019. The average age for the level at her gym was probably 10, with a pretty small range from 9 (mine + one other girl) to 11. She was a level 10 by 7th grade after choosing to repeat level 8 due to the season being cut short for COVID.
Meanwhile, at the same gym just a few years later, my younger DD did level 7 turned 12 in the middle of the season (2024) and was the average age for the level at her gym (age range 11-13).
I also noticed that at meets, my older DD was always in the youngest age group and often one of the youngest kids. I've been surprised to see that my younger DD who is doing the levels at an older age is never placed in an age group higher than the 2nd youngest, with the exception of states and regionals. That said, I wonder if there is a more universal shift to being a bit older. Maybe this is by default because these kids were slowed down in early levels due to COVID? Either way, I'm thankful for it! I think being a bit older in optionals is much healthier in all aspects. My older DD did 2 years of level 10 before hitting high school and then burnt out and quit!