Any age. We did a day at MK with my daughter when she was a year and 9 months old and i'll never forget the look on her face and her reactions when she met Mickey the first time. Plenty of rides she could do too. 40 inches is the first major benchmark for the majority of rides. Only a few are higher - RNRC (48), Space Mtn (44), FOP (44) and Everest (44)
My comment was in regards to the Giant Wheel, not Boomerang.
Last I knew they ran 2 on Tantrum pretty consistently. ROS is the only one without a second train available I believe.
We did the 2021 post covid Halloween party that was essentially an after hours event. Everything was a walk on except SDMT I believe (due to overflow from day guests)
If you're a carousel fan, a trip to the Herschell Factory Museum in North Tonawanda, NY is a must do. NT is also the home of Wurlitzer but I dont think there's any public display for it, the Wurlitzer Factory Park is mostly a mixed use development.