K.A.
What type of dolls? Baby dolls, Barbie?
I still have dolls and I'm 43. Mine are far more expensive now though. Look up Blythe and you can see what some of my dolls are ;) I was still playing with my Barbies when I was 12 or so. The way I played changed as I got older though.
I love playing with my daughter when she plays with her dolls. She's only 4.5 right now but she loves her dolls, all types.
There is no reason to force them to stop playing with them if they are enjoying it just because of some made up age of being "too old". If she doesn't want to play with them, let it be her choice.