I think it also depends on how well they know the park. A kid that has been to WDW 1 or 2 times or never I would not let roam the parks much. A kid that knows the parks well I would let go off at 12-13, if I was in the same park. I once let a group of my kids plus friends ages 16,15,15,13( they were all to stay together) go on their own basically all week, and they used the late EMH, and transportation sometimes 2am when they came in. I was a wreck but they were having the times of their lives.