I mistakenly took my DDs who were 5 and 7 at the time on it our first year without realizing how intense it was. They spent the entire ride with their heads down, clutching me, terrified. The younger one went on it again the next year at 6 just to see if it was as bad as she remembered. It was. She is an adventurous child and a dare devil. She went on RNR 4 times last year. Dino is the only ride she won't go on at Disney.
It's a different kind of scary than rollercoasters. I think it's more like the intensity of scary movies, haunted houses or scare actors only Dinos and there's no blood or gore.