DS rode it at 4 and loved it, then at 5 he refused to ride it. Make them see videos of the ride (real POV ones) and decide if they really will like it. At that age I will be more concerned with their tolerance for wait lines. Not sure at what time of the year you are going but in the summer even with fast pass or at rope drop you may be in for more than an under 5 kid can handle before they start to get impatient (which in my experience is ~ 20 minutes). Also, will they be OK with a 2 minute ride they cannot get on again if they love it unless they do another really long line? (learned this the hard way, I was that mom that had to take his 4 yo screaming out of 7DMT because he wanted to ride again and refused to get off). I think 7DMT is bumpier than people make it seem though, but I rode it 5 months pregnant, so that may be why.