For a 9-year-old to be in a stroller, it's all about the parents. Sorry! That's a parent who is more interested in doing everything THEY want to do, rather than taking it at a child's pace. Yes, a 9-year-old may get tired, so you take a break and have a snack. Or maybe they can't do rope drop until closing--so you don't. Or maybe they need a break midday.
My kid were 5 and 7 on our first trip and the thought of a stroller wasn't even on the radar. And they never would have gotten in one if I had suggested it! Certainly by 3rd grade, they would have laughed at the idea, thinking I was making a joke!
Sorry, if they got a little tired at 5 or 7, we took a break. Yes, maybe we walked a little slower. Maybe we didn't get to do every single thing in every single park. But we enjoyed family time together at a pace that worked for everyone. We didn't see night time shows every night and that was okay! We didn't race from ride to ride. We took our time and enjoyed things along the way. We strolled hand in hand, pointing out things here and there.
Strollers at that age have nothing to do with the kids--it's all about the parents. (And I will state, although it shouldn't be necessary, that this is for able-bodied kids. Anyone with physical issues is a different story, of course.)