It's 7 to ride alone without question. DGD rode tons of rides alone starting at 7, rides that DH and I hate like Barnstormer and Primeval Whirl, to name a few. The issue becomes what age can they ride together. That may be where you came in to issues, the 2 of them riding together, without an adult. Had they been single children it wouldn't be an issue. Not sure, just guessing. Because it's age 7 and up that can ride alone for sure.