We (my 4 1/2 yr old and 9 yr old daughters) did this on our Thanksgiving trip last year.
I thought I would be bored, but I really enjoyed it. Rose Petal and the Baron put on quite an entertaining show.
As far as age goes.....I really had to twist my 9 yr old's arm when I was planning this - she did not want to go, thought it would be babyish. She and I wound up loving it! My 4 yr old that REALLY wanted to go when I told her about it originally, got a bit squirrely and could have left half way thru. She did like it, but it was a bit long for her to sit.
Aurora shows up toward the end and visits with each table, signs autographs and poses for pics, and leads the girls in a dance. Mostly it is stories and songs performed by a very talented Rose Petal.
The girls got some cute parting gifts and it was a very special event.
Only you know your daughter and how long she would be able to sit and behave like a princess.

There were girls of all ages at the party we attended, but my 4 yr old is just a spunky monkey and would rather be up playing and moving around than sitting and listening to stories, etc for an hour and a half (or 2).
Happy planning -
Lives4Disney
