So just a little update to help anyone who might experience the same thing. I bought two adult tickets and tried to assign one to my 9 yo daughter's profile. As I feared it wouldn't let me me assign it to her because of the age issue. After calling Disney they said I could only assign it to her once she turned 10 which means I couldn't get FPs for her at 60+10 days for our reservation.
My workaround, without telling Disney, was that I went in and changed the birthday on her profile to show that she's 10 already and then I'll try to change it back to her real birthday after she turns 10. We'll see how that goes.