I have begun to look around for places which allow, or perhaps even emphasize, mixed-age classes. My dd's preschool class that she is starting in a week will have 3-5 year olds, keeping my fingers crossed that she will fit in there somewhere. Ds9's ballet classes are very mixed-age; with boys there usually are so few, the range of ages tends to stretch further. It seems good for all the kids, they all seem to have different strengths - humor, flexibility, better memory for steps, strength and so on. I think even the teachers appreciate being able to look to a certain child as a good model for a particular aspect of dance.
Maybe smaller places with fewer students will naturally tend towards broader age range classes.
Otoh, I know that things like pointe, and possibly some other parts of dance can not be taught to kids until their bodies are sufficiently mature, so perhaps there are some safety issues that your school is considering, but they need to share with you.
